dbi(3)

NAME

DBI - Database independent interface for Perl

SYNOPSIS

use DBI;
@driver_names = DBI->available_drivers;
@data_sources = DBI->data_sources($driver_name, attr);
$dbh = DBI->connect($data_source, $username, $auth,  attr);
$rv  = $dbh->do($statement);
$rv  = $dbh->do($statement, attr);
$rv  = $dbh->do($statement, attr, @bind_values);
$ary_ref  = $dbh->selectall_arrayref($statement);
$hash_ref      =     $dbh->selectall_hashref($statement,
$key_field);
$ary_ref = $dbh->selectcol_arrayref($statement);
$ary_ref = $dbh->selectcol_arrayref($statement, attr);
@row_ary  = $dbh->selectrow_array($statement);
$ary_ref  = $dbh->selectrow_arrayref($statement);
$hash_ref = $dbh->selectrow_hashref($statement);
$sth = $dbh->prepare($statement);
$sth = $dbh->prepare_cached($statement);
$rc = $sth->bind_param($p_num, $bind_value);
$rc = $sth->bind_param($p_num, $bind_value, $bind_type);
$rc = $sth->bind_param($p_num, $bind_value, attr);
$rv = $sth->execute;
$rv = $sth->execute(@bind_values);
$rc  =  $sth->bind_param_array($p_num, $bind_values, attr);
$rv = $sth->execute_array(attr);
$rv = $sth->execute_array(attr, @bind_values);
$rc = $sth->bind_col($col_num, ol_variable);
$rc = $sth->bind_columns(@list_of_refs_to_vars_to_bind);
@row_ary  = $sth->fetchrow_array;
$ary_ref  = $sth->fetchrow_arrayref;
$hash_ref = $sth->fetchrow_hashref;
$ary_ref  = $sth->fetchall_arrayref;
$ary_ref   =  $sth->fetchall_arrayref( $slice, $max_rows
);
$hash_ref = $sth->fetchall_hashref( $key_field );
$rv  = $sth->rows;
$rc  = $dbh->begin_work;
$rc  = $dbh->commit;
$rc  = $dbh->rollback;
$quoted_string = $dbh->quote($string);
$rc  = $h->err;
$str = $h->errstr;
$rv  = $h->state;
$rc  = $dbh->disconnect;
This synopsis above only lists the major methods.
GETTING HELP
If you have questions about DBI, you can get help from the
dbi-users@perl.org mailing list.  You can get help on sub
scribing and using the list by emailing:
dbi-users-help@perl.org
Also worth a visit is the DBI home page at:
http://dbi.perl.org/
Before asking any questions, reread this document, consult
the archives and read the DBI FAQ. The archives are listed
at the end of this document and on the DBI home page.  The
FAQ is installed as a DBI::FAQ module so you can read it
by executing "perldoc DBI::FAQ".
This document often uses terms like references, objects,
methods.  If you're not familar with those terms then it
would be a good idea to read at least the following perl
manuals first: perlreftut, perldsc, perllol, and perlboot.
Please note that Tim Bunce does not maintain the mailing
lists or the web page (generous volunteers do that).  So
please don't send mail directly to him; he just doesn't
have the time to answer questions personally. The dbiusers mailing list has lots of experienced people who
should be able to help you if you need it. If you do email
Tim he's very likely to just forward it to the mailing
list.
NOTES
This is the DBI specification that corresponds to the DBI
version 1.30 ("$Date: 2002/07/18 14:23:44 $").
The DBI is evolving at a steady pace, so it's good to
check that you have the latest copy.
The significant user-visible changes in each release are
documented in the DBI::Changes module so you can read them
by executing "perldoc DBI::Changes".
Some DBI changes require changes in the drivers, but the
drivers can take some time to catch up. Recent versions of
the DBI have added new features (generally marked NEW in
the text) that may not yet be supported by the drivers you
use. Talk to the authors of those drivers if you need the
new features.
Extensions to the DBI API often use the "DBIx::*" names
pace.  See "Naming Conventions and Name Space" and:
http://search.cpan.org/search?mode=module&query=DBIx%3A%3A

DESCRIPTION

The DBI is a database access module for the Perl program
ming language. It defines a set of methods, variables,
and conventions that provide a consistent database inter
face, independent of the actual database being used.

It is important to remember that the DBI is just an inter
face. The DBI is a layer of "glue" between an application
and one or more database driver modules. It is the driver modules which do most of the real work. The DBI provides a
standard interface and framework for the drivers to oper
ate within.

Architecture of a DBI Application
|<- Scope of DBI ->
.-. .--------------. .-------------.
.-------. | |---| XYZ Driver |---| XYZ Engine
| Perl | | | `--------------' `-------------'
| script| |A| |D| .--------------. .-------------.
| using |--|P|--|B|---|Oracle Driver |---|Oracle Engine
| DBI | |I| |I| `--------------' `-------------'
| API | | |...
|methods| | |... Other drivers
`-------' | |...
`-'
The API, or Application Programming Interface, defines the
call interface and variables for Perl scripts to use. The
API is implemented by the Perl DBI extension.
The DBI "dispatches" the method calls to the appropriate
driver for actual execution. The DBI is also responsible
for the dynamic loading of drivers, error checking and
handling, providing default implementations for methods,
and many other non-database specific duties.
Each driver contains implementations of the DBI methods
using the private interface functions of the corresponding
database engine. Only authors of sophisti
cated/multi-database applications or generic library func
tions need be concerned with drivers.
Notation and Conventions
The following conventions are used in this document:

$dbh Database handle object
$sth Statement handle object
$drh Driver handle object (rarely seen or used in ap
plications)
$h Any of the handle types above ($dbh, $sth, or
$drh)
$rc General Return Code (boolean: true=ok,
false=error)
$rv General Return Value (typically an integer)
@ary List of values returned from the database, typi
cally a row of data
$rows Number of rows processed (if available, else -1)
$fh A filehandle
undef NULL values are represented by undefined values
in Perl
attr Reference to a hash of attribute values passed to
methods
Note that Perl will automatically destroy database and
statement handle objects if all references to them are
deleted.
Outline Usage
To use DBI, first you need to load the DBI module:

use DBI;
use strict;
(The "use strict;" isn't required but is strongly
recommended.)
Then you need to "connect" to your data source and get a
handle for that connection:

$dbh = DBI->connect($dsn, $user, $password,
{ RaiseError => 1, AutoCommit => 0
});
Since connecting can be expensive, you generally just con
nect at the start of your program and disconnect at the
end.
Explicitly defining the required "AutoCommit" behavior is
strongly recommended and may become mandatory in a later
version. This determines whether changes are automati
cally committed to the database when executed, or need to
be explicitly committed later.
The DBI allows an application to "prepare" statements for
later execution. A prepared statement is identified by a
statement handle held in a Perl variable. We'll call the
Perl variable $sth in our examples.
The typical method call sequence for a "SELECT" statement
is:

prepare,
execute, fetch, fetch, ...
execute, fetch, fetch, ...
execute, fetch, fetch, ...
for example:

$sth = $dbh->prepare("SELECT foo, bar FROM table WHERE
baz=?");
$sth->execute( $baz );
while ( @row = $sth->fetchrow_array ) {
print "@row0;
}
The typical method call sequence for a non-"SELECT" state
ment is:

prepare,
execute,
execute,
execute.
for example:

$sth = $dbh->prepare("INSERT INTO table(foo,bar,baz)
VALUES (?,?,?)");
while(<CSV>) {
chomp;
my ($foo,$bar,$baz) = split /,/;
$sth->execute( $foo, $bar, $baz );
}
The "do()" method can be used for non repeated
non-"SELECT" statement (or with drivers that don't support
placeholders):

$rows_affected = $dbh->do("UPDATE your_table SET foo =
foo + 1");
To commit your changes to the database (when "AutoCommit"
is off):

$dbh->commit; # or call $dbh->rollback; to undo changes
Finally, when you have finished working with the data
source, you should "disconnect" from it:

$dbh->disconnect;
General Interface Rules & Caveats
The DBI does not have a concept of a "current session".
Every session has a handle object (i.e., a $dbh) returned
from the "connect" method. That handle object is used to
invoke database related methods.
Most data is returned to the Perl script as strings. (Null
values are returned as "undef".) This allows arbitrary
precision numeric data to be handled without loss of accu
racy. Beware that Perl may not preserve the same accuracy
when the string is used as a number.
Dates and times are returned as character strings in the
current default format of the corresponding database
engine. Time zone effects are database/driver dependent.
Perl supports binary data in Perl strings, and the DBI
will pass binary data to and from the driver without
change. It is up to the driver implementors to decide how
they wish to handle such binary data.
Most databases that understand multiple character sets
have a default global charset. Text stored in the database
is, or should be, stored in that charset; if not, then
that's the fault of either the database or the application
that inserted the data. When text is fetched it should be
automatically converted to the charset of the client, pre
sumably based on the locale. If a driver needs to set a
flag to get that behavior, then it should do so; it should
not require the application to do that.
Multiple SQL statements may not be combined in a single
statement handle ($sth), although some databases and
drivers do support this (notably Sybase and SQL Server).
Non-sequential record reads are not supported in this ver
sion of the DBI. In other words, records can only be
fetched in the order that the database returned them, and
once fetched they are forgotten.
Positioned updates and deletes are not directly supported
by the DBI. See the description of the "CursorName"
attribute for an alternative.
Individual driver implementors are free to provide any
private functions and/or handle attributes that they feel
are useful. Private driver functions can be invoked using
the DBI "func()" method. Private driver attributes are
accessed just like standard attributes.
Many methods have an optional "attr" parameter which can
be used to pass information to the driver implementing the
method. Except where specifically documented, the "attr"
parameter can only be used to pass driver specific hints.
In general, you can ignore "attr" parameters or pass it
as "undef".
Naming Conventions and Name Space
The DBI package and all packages below it ("DBI::*") are
reserved for use by the DBI. Extensions and related mod
ules use the "DBIx::" namespace (see
"http://www.perl.com/CPAN/modules/by-module/DBIx/").
Package names beginning with "DBD::" are reserved for use
by DBI database drivers. All environment variables used
by the DBI or by individual DBDs begin with ""DBI_"" or
""DBD_"".
The letter case used for attribute names is significant
and plays an important part in the portability of DBI
scripts. The case of the attribute name is used to sig
nify who defined the meaning of that name and its values.

Case of name Has a meaning defined by
------------ -----------------------UPPER_CASE Standards, e.g., X/Open, ISO SQL92 etc
(portable)
MixedCase DBI API (portable), underscores are not
used.
lower_case Driver or database engine specific (non
portable)
It is of the utmost importance that Driver developers only
use lowercase attribute names when defining private
attributes. Private attribute names must be prefixed with
the driver name or suitable abbreviation (e.g., ""ora_""
for Oracle, ""ing_"" for Ingres, etc).
Driver Specific Prefix Registry:

ad_ DBD::AnyData
ado_ DBD::ADO
best_ DBD::BestWins
csv_ DBD::CSV
db2_ DBD::DB2
f_ DBD::File
file_ DBD::TextFile
ib_ DBD::InterBase
ing_ DBD::Ingres
ix_ DBD::Informix
msql_ DBD::mSQL
mysql_ DBD::mysql
odbc_ DBD::ODBC
ora_ DBD::Oracle
pg_ DBD::Pg
proxy_ DBD::Proxy
rdb_ DBD::RDB
sapdb_ DBD::SAP_DB
solid_ DBD::Solid
syb_ DBD::Sybase
sql_ SQL::Statement (used by some drivers)
tdat_ DBD::Teradata
tuber_ DBD::Tuber
uni_ DBD::Unify
xbase_ DBD::XBase
SQL - A Query Language
Most DBI drivers require applications to use a dialect of
SQL (Structured Query Language) to interact with the
database engine. The following links provide useful
information and further links about SQL:

http://www.altavista.com/query?q=sql+tutorial
http://www.jcc.com/sql_stnd.html
http://www.contrib.andrew.cmu.edu/~shadow/sql.html
The DBI itself does not mandate or require any particular
language to be used; it is language independent. In ODBC
terms, the DBI is in "pass-thru" mode, although individual
drivers might not be. The only requirement is that queries
and other statements must be expressed as a single string
of characters passed as the first argument to the "pre
pare" or "do" methods.
For an interesting diversion on the real history of RDBMS
and SQL, from the people who made it happen, see:

http://ftp.digital.com/pub/DEC/SRC/technical
notes/SRC-1997-018-html/sqlr95.html
Follow the "And the rest" and "Intergalactic dataspeak"
links for the SQL history.
Placeholders and Bind Values
Some drivers support placeholders and bind values. Place_
holders, also called parameter markers, are used to indi cate values in a database statement that will be supplied
later, before the prepared statement is executed. For
example, an application might use the following to insert
a row of data into the SALES table:

INSERT INTO sales (product_code, qty, price) VALUES (?,
?, ?)
or the following, to select the description for a product:

SELECT description FROM products WHERE product_code = ?
The "?" characters are the placeholders. The association
of actual values with placeholders is known as binding,
and the values are referred to as bind values.
When using placeholders with the SQL "LIKE" qualifier, you
must remember that the placeholder substitutes for the
whole string. So you should use ""... LIKE ? ..."" and
include any wildcard characters in the value that you bind
to the placeholder.
Null Values
Undefined values, or "undef", can be used to indicate null
values. However, care must be taken in the particular
case of trying to use null values to qualify a "SELECT"
statement. Consider:

SELECT description FROM products WHERE product_code = ?
Binding an "undef" (NULL) to the placeholder will not
select rows which have a NULL "product_code"! Refer to the
SQL manual for your database engine or any SQL book for
the reasons for this. To explicitly select NULLs you have
to say ""WHERE product_code IS NULL"" and to make that
general you have to say:

... WHERE (product_code = ? OR (? IS NULL AND prod
uct_code IS NULL))
and bind the same value to both placeholders.
Performance
Without using placeholders, the insert statement shown
previously would have to contain the literal values to be
inserted and would have to be re-prepared and re-executed
for each row. With placeholders, the insert statement only
needs to be prepared once. The bind values for each row
can be given to the "execute" method each time it's
called. By avoiding the need to re-prepare the statement
for each row, the application typically runs many times
faster. Here's an example:

my $sth = $dbh->prepare(q{
INSERT INTO sales (product_code, qty, price) VALUES
(?, ?, ?)
}) or die $dbh->errstr;
while (<>) {
chomp;
my ($product_code, $qty, $price) = split /,/;
$sth->execute($product_code, $qty, $price) or die
$dbh->errstr;
}
$dbh->commit or die $dbh->errstr;
See "execute" and "bind_param" for more details.
The "q{...}" style quoting used in this example avoids
clashing with quotes that may be used in the SQL state
ment. Use the double-quote like "qq{...}" operator if you
want to interpolate variables into the string. See "Quote
and Quote-like Operators" in perlop for more details.
See also the "bind_column" method, which is used to asso
ciate Perl variables with the output columns of a "SELECT"
statement.

THE DBI PACKAGE AND CLASS

In this section, we cover the DBI class methods, utility
functions, and the dynamic attributes associated with
generic DBI handles.

DBI Constants

Constants representing the values of the SQL standard
types can be imported individually by name, or all
together by importing the special ":sql_types" tag.

The names and values of all the defined SQL standard types
can be produced like this:
foreach (@{ $DBI::EXPORT_TAGS{sql_types} }) {
printf "%s=%d0, $_, &{"DBI::$_"};
}
These constants are defined by SQL/CLI, ODBC or both.
"SQL_BIGINT" is (currently) omitted, because SQL/CLI and
ODBC provide conflicting codes.
See the "type_info", "type_info_all", and "bind_param"
methods for possible uses.
Note that just because the DBI defines a named constant
for a given data type doesn't mean that drivers will sup
port that data type.
DBI Class Methods
The following methods are provided by the DBI class:
"connect"
$dbh = DBI->connect($data_source, $username, $pass
word)
or die $DBI::errstr;
$dbh = DBI->connect($data_source, $username, $pass
word, attr)
or die $DBI::errstr;
Establishes a database connection, or session, to the
requested $data_source. Returns a database handle
object if the connection succeeds. Use "$dbh-">"dis
connect" to terminate the connection.
If the connect fails (see below), it returns "undef"
and sets both $DBI::err and $DBI::errstr. (It does not
set $!, etc.) You should generally test the return
status of "connect" and "print $DBI::errstr" if it has
failed.
Multiple simultaneous connections to multiple
databases through multiple drivers can be made via the
DBI. Simply make one "connect" call for each database
and keep a copy of each returned database handle.
The $data_source value should begin with
""dbi:"driver_name":"". The driver_name specifies the driver that will be used to make the connection. (Let
ter case is significant.)
As a convenience, if the $data_source parameter is
undefined or empty, the DBI will substitute the value
of the environment variable "DBI_DSN". If just the
driver_name part is empty (i.e., the $data_source pre fix is ""dbi::""), the environment variable
"DBI_DRIVER" is used. If neither variable is set, then
"connect" dies.
Examples of $data_source values are:

dbi:DriverName:database_name
dbi:DriverName:database_name@hostname:port
dbi:DriverName:database=database_name;host=host
name;port=port
There is no standard for the text following the driver name. Each driver is free to use whatever syntax it
wants. The only requirement the DBI makes is that all
the information is supplied in a single string. You
must consult the documentation for the drivers you are
using for a description of the syntax they require.
(Where a driver author needs to define a syntax for
the $data_source, it is recommended that they follow
the ODBC style, shown in the last example above.)
If the environment variable "DBI_AUTOPROXY" is defined
(and the driver in $data_source is not ""Proxy"") then
the connect request will automatically be changed to:

dbi:Proxy:$ENV{DBI_AUTOPROXY};dsn=$data_source
and passed to the DBD::Proxy module. "DBI_AUTOPROXY"
is typically set as ""hostname=...;port=..."". See the
DBD::Proxy documentation for more details.
If $username or $password are undefined (rather than
just empty), then the DBI will substitute the values
of the "DBI_USER" and "DBI_PASS" environment vari
ables, respectively. The DBI will warn if the envi
ronment variables are not defined. However, the
everyday use of these environment variables is not
recommended for security reasons. The mechanism is
primarily intended to simplify testing.
"DBI-">"connect" automatically installs the driver if
it has not been installed yet. Driver installation
either returns a valid driver handle, or it dies with
an error message that includes the string
""install_driver"" and the underlying problem. So
"DBI-">"connect" will die on a driver installation
failure and will only return "undef" on a connect
failure, in which case $DBI::errstr will hold the
error message.
The $data_source argument (with the ""dbi:...:"" pre
fix removed) and the $username and $password arguments
are then passed to the driver for processing. The DBI
does not define any interpretation for the contents of
these fields. The driver is free to interpret the
$data_source, $username, and $password fields in any
way, and supply whatever defaults are appropriate for
the engine being accessed. (Oracle, for example, uses
the ORACLE_SID and TWO_TASK environment variables if
no $data_source is specified.)
The "AutoCommit" and "PrintError" attributes for each
connection default to "on". (See "AutoCommit" and
"PrintError" for more information.) However, it is
strongly recommended that you explicitly define "Auto
Commit" rather than rely on the default. Future ver
sions of the DBI may issue a warning if "AutoCommit"
is not explicitly defined.
The "attr" parameter can be used to alter the
default settings of "PrintError", "RaiseError", "Auto
Commit", and other attributes. For example:

$dbh = DBI->connect($data_source, $user, $pass, {
PrintError => 0,
AutoCommit => 0
});
You can also define connection attribute values within
the $data_source parameter. For example:

dbi:DriverName(PrintError=>0,Taint=>1):...
Individual attributes values specified in this way
take precedence over any conflicting values specified
via the "attr" parameter to "connect".
The "dbi_connect_method" attribute can be used to
specify which driver method should be called to estab
lish the connection. The only useful values are 'con
nect', 'connect_cached', or some specialized case like
'Apache::DBI::connect' (which is automatically the
default when running within Apache).
Where possible, each session ($dbh) is independent
from the transactions in other sessions. This is use
ful when you need to hold cursors open across transac
tions--for example, if you use one session for your
long lifespan cursors (typically read-only) and
another for your short update transactions.
For compatibility with old DBI scripts, the driver can
be specified by passing its name as the fourth argu
ment to "connect" (instead of "attr"):

$dbh = DBI->connect($data_source, $user, $pass,
$driver);
In this "old-style" form of "connect", the
$data_source should not start with
""dbi:driver_name:"". (If it does, the embedded
driver_name will be ignored). Also note that in this
older form of "connect", the "$dbh-">"{AutoCommit}"
attribute is undefined, the "$dbh-">"{PrintError}" attribute is off, and the old "DBI_DBNAME" environment
variable is checked if "DBI_DSN" is not defined.
Beware that this "old-style" "connect" will be with
drawn in a future version of DBI.
"connect_cached" NEW
$dbh = DBI->connect_cached($data_source, $username,
$password)
or die $DBI::errstr;
$dbh = DBI->connect_cached($data_source, $username,
$password, attr)
or die $DBI::errstr;
"connect_cached" is like "connect", except that the
database handle returned is also stored in a hash
associated with the given parameters. If another call
is made to "connect_cached" with the same parameter
values, then the corresponding cached $dbh will be
returned if it is still valid. The cached database
handle is replaced with a new connection if it has
been disconnected or if the "ping" method fails.
Note that the behavior of this method differs in sev
eral respects from the behavior of presistent connec
tions implemented by Apache::DBI.
Caching can be useful in some applications, but it can
also cause problems and should be used with care. The
exact behavior of this method is liable to change, so
if you intend to use it in any production applications
you should discuss your needs on the dbi-users mailing list.
The cache can be accessed (and cleared) via the
"CachedKids" attribute.
"available_drivers"
@ary = DBI->available_drivers;
@ary = DBI->available_drivers($quiet);
Returns a list of all available drivers by searching
for "DBD::*" modules through the directories in @INC.
By default, a warning is given if some drivers are
hidden by others of the same name in earlier directo
ries. Passing a true value for $quiet will inhibit the
warning.
"data_sources"
@ary = DBI->data_sources($driver);
@ary = DBI->data_sources($driver, attr);
Returns a list of all data sources (databases) avail
able via the named driver. If $driver is empty or
"undef", then the value of the "DBI_DRIVER" environ
ment variable is used.
The driver will be loaded if it hasn't been already.
Note that if the driver loading fails then it dies
with an error message that includes the string
""install_driver"" and the underlying problem.
Data sources are returned in a form suitable for pass
ing to the "connect" method (that is, they will
include the ""dbi:$driver:"" prefix).
Note that many drivers have no way of knowing what
data sources might be available for it. These drivers
return an empty or incomplete list or may require
driver-specific attributes, such as a connected
database handle, to be supplied.
"trace"
DBI->trace($trace_level)
DBI->trace($trace_level, $trace_filename)
DBI trace information can be enabled for all handles
using the "trace" DBI class method. To enable trace
information for a specific handle, use the similar
"$h-">"trace" method described elsewhere.
Trace levels are as follows:

0 - Trace disabled.
1 - Trace DBI method calls returning with results or
errors.
2 - Trace method entry with parameters and returning
with results.
3 - As above, adding some high-level information
from the driver
and some internal information from the DBI.
4 - As above, adding more detailed information from
the driver.
5 and above - As above but with more and more ob
scure information.
Trace level 1 is best for a simple overview of what's
happening. Trace level 2 is a good choice for general
purpose tracing. Levels 3 and above (up to 9) are
best reserved for investigating a specific problem,
when you need to see "inside" the driver and DBI.
The trace output is detailed and typically very use
ful. Much of the trace output is formatted using the
"neat" function, so strings in the trace output may be
edited and truncated.
Initially trace output is written to "STDERR". If
$trace_filename is specified and can be opened in
append mode then all trace output (including that from
other handles) is redirected to that file. A warning
is generated is the file can't be opened. Further
calls to "trace" without a $trace_filename do not
alter where the trace output is sent. If $trace_file
name is undefined, then trace output is sent to
"STDERR" and the previous trace file is closed. The
"trace" method returns the previous tracelevel.
See also the "$h-">"trace" and "$h-">"trace_msg" meth
ods and the "DEBUGGING" section for information about
the "DBI_TRACE" environment variable.
DBI Utility Functions
In addition to the methods listed in the previous section,
the DBI package also provides these utility functions:
"neat"
$str = DBI::neat($value, $maxlen);
Return a string containing a neat (and tidy) represen
tation of the supplied value.
Strings will be quoted, although internal quotes will
not be escaped. Values known to be numeric will be
unquoted. Undefined (NULL) values will be shown as
"undef" (without quotes). Unprintable characters will
be replaced by dot (.).
For result strings longer than $maxlen the result
string will be truncated to "$maxlen-4" and ""...'""
will be appended. If $maxlen is 0 or "undef", it
defaults to $DBI::neat_maxlen which, in turn, defaults
to 400.
This function is designed to format values for human
consumption. It is used internally by the DBI for
"trace" output. It should typically not be used for
formatting values for database use. (See also
"quote".)
"neat_list"
$str = DBI::neat_list(@listref, $maxlen,
$field_sep);
Calls "DBI::neat" on each element of the list and
returns a string containing the results joined with
$field_sep. $field_sep defaults to ", ".
"looks_like_number"
@bool = DBI::looks_like_number(@array);
Returns true for each element that looks like a num
ber. Returns false for each element that does not
look like a number. Returns "undef" for each element
that is undefined or empty.
"hash"
$hash_value = DBI::hash($buffer, $type);
Return a 32-bit integer 'hash' value corresponding to
the contents of $buffer. The $type parameter selects
which kind of hash algorithm should be used.
For the technically curious, type 0 (which is the
default if $type isn't specified) is based on the Perl
5.1 hash except that the value is forced to be nega
tive (for obscure historical reasons). Type 1 is the
better "Fowler / Noll / Vo" (FNV) hash. See
http://www.isthe.com/chongo/tech/comp/fnv/ for more
information. Both types are implemented in C and are
very fast.
This function doesn't have much to do with databases,
except that it can be handy to store hash values in a
database.
DBI Dynamic Attributes
Dynamic attributes are always associated with the last
handle used (that handle is represented by $h in the descriptions below).
Where an attribute is equivalent to a method call, then
refer to the method call for all related documentation.
Warning: these attributes are provided as a convenience
but they do have limitations. Specifically, they have a
short lifespan: because they are associated with the last
handle used, they should only be used immediately after calling the method that "sets" them. If in any doubt, use
the corresponding method call.
$DBI::err
Equivalent to "$h-">"err".
$DBI::errstr
Equivalent to "$h-">"errstr".
$DBI::state
Equivalent to "$h-">"state".
$DBI::rows
Equivalent to "$h-">"rows". Please refer to the docu
mentation for the "rows" method.
$DBI::lasth
Returns the DBI object handle used for the most recent
DBI method call. If the last DBI method call was a
DESTROY then $DBI::lasth will return the handle of the
parent of the destroyed handle, if there is one.

METHODS COMMON TO ALL HANDLES

The following methods can be used by all types of DBI han
dles.

"err"
$rv = $h->err;
Returns the native database engine error code from the last driver method called. The code is typically an
integer but you should not assume that.
The DBI resets $h->err to undef before most DBI method
calls, so the value only has a short lifespan. Also,
most drivers share the same error variables across all
their handles, so calling a method on one handle will
typically reset the error on all the other handles
that are children of that driver.
If you need to test for individual errors and have
your program be portable to different database
engines, then you'll need to determine what the corre
sponding error codes are for all those engines and
test for all of them.
"errstr"
$str = $h->errstr;
Returns the native database engine error message from
the last driver method called. This has the same
lifespan issues as the "err" method described above.
"state"
$str = $h->state;
Returns an error code in the standard SQLSTATE five
character format. Note that the specific success code
00000 is translated to '' (false). If the driver does
not support SQLSTATE (and most don't), then state will
return "S1000" (General Error) for all errors.
The driver is free to return any value via "state",
e.g., warning codes, even if it has not declared an
error by returning a true value via the "err" method
described above.
"set_err" NEW
$rv = $h->set_err($err, $errstr);
$rv = $h->set_err($err, $errstr, $state, $method);
$rv = $h->set_err($err, $errstr, $state, $method,
$rv);
Set the "err", "errstr", and "state" values for the
handle. This will trigger the normal DBI error han
dling mechanisms, such as "RaiseError" and "HandleEr
ror", if they are enabled. This method is typically
only used by DBI drivers and DBI subclasses.
The $method parameter provides an alternate method
name, instead of the fairly unhelpful '"set_err"', for
the "RaiseError"/"PrintError" error string.
The "set_err" method normally returns undef. The $rv
parameter provides an alternate return value. The
"HandleError" subroutine can access and alter this
value.
"trace"
$h->trace($trace_level);
$h->trace($trace_level, $trace_filename);
DBI trace information can be enabled for a specific
handle (and any future children of that handle) by
setting the trace level using the "trace" method.
Trace level 1 is best for a simple overview of what's
happening. Trace level 2 is a good choice for general
purpose tracing. Levels 3 and above (up to 9) are
best reserved for investigating a specific problem,
when you need to see "inside" the driver and DBI. Set
$trace_level to 0 to disable the trace.
The trace output is detailed and typically very use
ful. Much of the trace output is formatted using the
"neat" function, so strings in the trace output may be
edited and truncated.
Initially, trace output is written to "STDERR". If
$trace_filename is specified, then the file is opened
in append mode and all trace output (including that
from other handles) is redirected to that file. Fur
ther calls to trace without a $trace_filename do not
alter where the trace output is sent. If $trace_file
name is undefined, then trace output is sent to
"STDERR" and the previous trace file is closed.
See also the "DBI-">"trace" method, the
"$h-">"{TraceLevel}" attribute, and "DEBUGGING" for
information about the "DBI_TRACE" environment vari
able.
"trace_msg"
$h->trace_msg($message_text);
$h->trace_msg($message_text, $min_level);
Writes $message_text to the trace file if trace is
enabled for $h or for the DBI as a whole. Can also be
called as "DBI-">"trace_msg($msg)". See "trace".
If $min_level is defined, then the message is output
only if the trace level is equal to or greater than
that level. $min_level defaults to 1.
"func"
$h->func(@func_arguments, $func_name) or die ...;
The "func" method can be used to call private nonstandard and non-portable methods implemented by the
driver. Note that the function name is given as the
last argument.
It's also important to note that the func() method
does not clear a previous error ($DBI::err etc.) and
it does not trigger automatic error detection
(RaiseError etc.) so you must check the return status
and/or $h->err to detect errors.
(This method is not directly related to calling stored
procedures. Calling stored procedures is currently
not defined by the DBI. Some drivers, such as
DBD::Oracle, support it in non-portable ways. See
driver documentation for more details.)

ATTRIBUTES COMMON TO ALL HANDLES

These attributes are common to all types of DBI handles.

Some attributes are inherited by child handles. That is,
the value of an inherited attribute in a newly created
statement handle is the same as the value in the parent
database handle. Changes to attributes in the new state
ment handle do not affect the parent database handle and
changes to the database handle do not affect existing
statement handles, only future ones.

Attempting to set or get the value of an unknown attribute
is fatal, except for private driver specific attributes
(which all have names starting with a lowercase letter).

Example:
$h->{AttributeName} = ...; # set/write
... = $h->{AttributeName}; # get/read
"Warn" (boolean, inherited)
Enables useful warnings for certain bad practices.
Enabled by default. Some emulation layers, especially
those for Perl 4 interfaces, disable warnings. Since
warnings are generated using the Perl "warn" function,
they can be intercepted using the Perl $SIG{__WARN__}
hook.
"Active" (boolean, read-only)
True if the handle object is "active". This is rarely
used in applications. The exact meaning of active is
somewhat vague at the moment. For a database handle it
typically means that the handle is connected to a
database ("$dbh-">"disconnect" sets "Active" off).
For a statement handle it typically means that the
handle is a "SELECT" that may have more data to fetch.
(Fetching all the data or calling "$sth-">"finish"
sets "Active" off.)
"Kids" (integer, read-only)
For a driver handle, "Kids" is the number of currently
existing database handles that were created from that
driver handle. For a database handle, "Kids" is the
number of currently existing statement handles that
were created from that database handle.
"ActiveKids" (integer, read-only)
Like "Kids", but only counting those that are "Active"
(as above).
"CachedKids" (hash ref)
For a database handle, returns a reference to the
cache (hash) of statement handles created by the "pre
pare_cached" method. For a driver handle, returns a
reference to the cache (hash) of database handles cre
ated by the "connect_cached" method.
"CompatMode" (boolean, inherited)
Used by emulation layers (such as Oraperl) to enable
compatible behavior in the underlying driver (e.g.,
DBD::Oracle) for this handle. Not normally set by
application code.
"InactiveDestroy" (boolean)
This attribute can be used to disable the database engine related effect of DESTROYing a handle (which
would normally close a prepared statement or discon
nect from the database etc).
For a database handle, this attribute does not disable
an explicit call to the disconnect method, only the implicit call from DESTROY.
The default value, false, means that a handle will be
automatically destroyed when it passes out of scope.
A true value disables automatic destruction. (Think of
the name as meaning 'inactive the DESTROY method'.)
This attribute is specifically designed for use in
Unix applications that "fork" child processes. Either
the parent or the child process, but not both, should
set "InactiveDestroy" on all their shared handles.
Note that some databases, including Oracle, don't sup
port passing a database connection across a fork.
"PrintError" (boolean, inherited)
This attribute can be used to force errors to generate
warnings (using "warn") in addition to returning error
codes in the normal way. When set "on", any method
which results in an error occuring will cause the DBI
to effectively do a "warn("$class $method failed:
$DBI::errstr")" where $class is the driver class and
$method is the name of the method which failed. E.g.,

DBD::Oracle::db prepare failed: ... error text here
...
By default, "DBI-">"connect" sets "PrintError" "on".
If desired, the warnings can be caught and processed
using a $SIG{__WARN__} handler or modules like
CGI::Carp and CGI::ErrorWrap.
"RaiseError" (boolean, inherited)
This attribute can be used to force errors to raise
exceptions rather than simply return error codes in
the normal way. It is "off" by default. When set
"on", any method which results in an error will cause
the DBI to effectively do a "die("$class $method
failed: $DBI::errstr")", where $class is the driver
class and $method is the name of the method that
failed. E.g.,

DBD::Oracle::db prepare failed: ... error text here
...
If you turn "RaiseError" on then you'd normally turn
"PrintError" off. If "PrintError" is also on, then
the "PrintError" is done first (naturally).
Typically "RaiseError" is used in conjunction with
"eval { ... }" to catch the exception that's been
thrown and followed by an "if ($@) { ... }" block to
handle the caught exception. In that eval block the
$DBI::lasth variable can be useful for diagnosis and
reporting. For example, $DBI::lasth->{Type} and
$DBI::lasth->{Statement}.
If you want to temporarily turn "RaiseError" off
(inside a library function that is likely to fail, for
example), the recommended way is like this:

{
local $h->{RaiseError}; # localize and turn off
for this block
...
}
The original value will automatically and reliably be
restored by Perl, regardless of how the block is
exited. The same logic applies to other attributes,
including "PrintError".
Sadly, this doesn't work for Perl versions up to and
including 5.004_04. Even more sadly, for Perl 5.5 and
5.6.0 it does work but leaks memory! For backwards
compatibility, you could just use "eval { ... }"
instead.
"HandleError" (code ref, inherited)
This attribute can be used to provide your own alter
native behaviour in case of errors. If set to a refer
ence to a subroutine then that subroutine is called
when an error is detected (at the same point that
"RaiseError" and "PrintError" are handled).
The subroutine is called with three parameters: the
error message string that "RaiseError" and "PrintEr
ror" would use, the DBI handle being used, and the
first value being returned by the method that failed
(typically undef).
If the subroutine returns a false value then the
"RaiseError" and/or "PrintError" attributes are
checked and acted upon as normal.
For example, to "die" with a full stack trace for any
error:

use Carp;
$h->{HandleError} = sub { confess(shift) };
Or to turn errors into exceptions:

use Exception; # or your own favourite exception
module
$h->{HandleError} = sub { Excep
tion->new('DBI')->raise($_[0]) };
It is possible to 'stack' multiple HandleError han
dlers by using closures:

sub your_subroutine {
my $previous_handler = $h->{HandleError};
$h->{HandleError} = sub {
return 1 if $previous_handler and &$previ
ous_handler(@_);
... your code here ...
}
}
Using a "my" inside a subroutine to store the previous
"HandleError" value is important. See perlsub and
perlref for more information about closures.
It is possible for "HandleError" to alter the error
message that will be used by "RaiseError" and "Print
Error" if it returns false. It can do that by alter
ing the value of $_[0]. This example appends a stack
trace to all errors and, unlike the previous example
using Carp::confess, this will work "PrintError" as
well as "RaiseError":

$h->{HandleError} = sub {
$_[0]=Carp::longmess($_[0]); 0; };
It is also possible for "HandleError" to hide an
error, to a limited degree, by using "set_err" to
reset $DBI::err and $DBI::errstr, and altering the
return value of the failed method. For example:

$h->{HandleError} = sub {
return 0 unless $_[0] =~ /^ fetchrow_arrayref
failed:/;
return 0 unless $_[1]->err == 1234; # the error to
'hide'
$h->set_err(0,""); # turn off the error
$_[2] = [ ... ]; # supply alternative return
value
return 1;
};
This only works for methods which return a single
value and is hard to make reliable (avoiding infinite
loops, for example) and so isn't recommended for gen
eral use! If you find a good use for it then please
let me know.
"ShowErrorStatement" (boolean, inherited) NEW
This attribute can be used to cause the relevant
Statement text to be appended to the error messages
generated by the "RaiseError" and "PrintError"
attributes. Only applies to errors on statement han
dles plus the prepare(), do(), and the various "select*()" database handle methods. (The exact for
mat of the appended text is subject to change.)
If "$h->{ParamValues}" returns a hash reference of
parameter (placeholder) values then those are format
ted and appened to the end of the Statement text in
the error message.
"TraceLevel" (integer, inherited) NEW
This attribute can be used as an alternative to the
"trace" method to set the DBI trace level for a spe
cific handle.
"FetchHashKeyName" (string, inherited)
This attribute is used to specify which attribute name
the fetchrow_hashref() method should use to get the field names for the hash keys. For historical reasons
it defaults to '"NAME"' but it is recommended to set
it to '"NAME_lc"' or '"NAME_uc"' according to your
preference. It can only be set for driver and database
tables. For statement handles the value is frozen
when prepare() is called.
"ChopBlanks" (boolean, inherited)
This attribute can be used to control the trimming of
trailing space characters from fixed width character
(CHAR) fields. No other field types are affected, even
where field values have trailing spaces.
The default is false (although it is possible that the
default may change). Applications that need specific
behavior should set the attribute as needed. Emulation
interfaces should set the attribute to match the
behavior of the interface they are emulating.
Drivers are not required to support this attribute,
but any driver which does not support it must arrange
to return "undef" as the attribute value.
"LongReadLen" (unsigned integer, inherited)
This attribute may be used to control the maximum
length of long fields ("blob", "memo", etc.) which the
driver will read from the database automatically when
it fetches each row of data. The "LongReadLen"
attribute only relates to fetching and reading long
values; it is not involved in inserting or updating
them.
A value of 0 means not to automatically fetch any long
data. ("fetch" should return "undef" for long fields
when "LongReadLen" is 0.)
The default is typically 0 (zero) bytes but may vary
between drivers. Applications fetching long fields
should set this value to slightly larger than the
longest long field value to be fetched.
Some databases return some long types encoded as pairs
of hex digits. For these types, "LongReadLen" relates
to the underlying data length and not the doubled-up
length of the encoded string.
Changing the value of "LongReadLen" for a statement
handle after it has been "prepare"'d will typically
have no effect, so it's common to set "LongReadLen" on
the $dbh before calling "prepare".
Note that the value used here has a direct effect on
the memory used by the application, so don't be too
generous.
See "LongTruncOk" for more information on truncation
behavior.
"LongTruncOk" (boolean, inherited)
This attribute may be used to control the effect of
fetching a long field value which has been truncated
(typically because it's longer than the value of the
"LongReadLen" attribute).
By default, "LongTruncOk" is false and so fetching a
long value that needs to be truncated will cause the
fetch to fail. (Applications should always be sure to
check for errors after a fetch loop in case an error,
such as a divide by zero or long field truncation,
caused the fetch to terminate prematurely.)
If a fetch fails due to a long field truncation when
"LongTruncOk" is false, many drivers will allow you to
continue fetching further rows.
See also "LongReadLen".
"Taint" (boolean, inherited)
If this attribute is set to a true value and Perl is
running in taint mode (e.g., started with the "-T"
option), then all data fetched from the database is
tainted, and the arguments to most DBI method calls
are checked for being tainted. This may change.
The attribute defaults to off, even if Perl is in
taint mode. See perlsec for more about taint mode.
If Perl is not running in taint mode, this attribute
has no effect.
When fetching data that you trust you can turn off the
Taint attribute, for that statement handle, for the
duration of the fetch loop.
Currently only fetched data is tainted. It is possible
that the results of other DBI method calls, and the
value of fetched attributes, may also be tainted in
future versions. That change may well break your
applications unless you take great care now. If you
use DBI Taint mode, please report your experience and
any suggestions for changes.
"Profile" (inherited)
Enable collection and reporting of method call timing
statistics. See the DBI::Profile module documentation
for much more detail.
"private_your_module_name_*"
The DBI provides a way to store extra information in a
DBI handle as "private" attributes. The DBI will allow
you to store and retreive any attribute which has a
name starting with ""private_"".
It is strongly recommended that you use just one pri vate attribute (e.g., use a hash ref) and give it a
long and unambiguous name that includes the module or
application name that the attribute relates to (e.g.,
""private_YourFullModuleName_thingy"").
Because of the way the Perl tie mechanism works you
cannot reliably use the "||=" operator directly to
initialise the attribute, like this:

my $foo = $dbh->{private_yourmodname_foo} ||= { ...
}; # WRONG
you should use a two step approach like this:

my $foo = $dbh->{private_yourmodname_foo};
$foo ||= $dbh->{private_yourmodname_foo} = { ... };

DBI DATABASE HANDLE OBJECTS

This section covers the methods and attributes associated
with database handles.

Database Handle Methods

The following methods are specified for DBI database han
dles:

"do"
$rows = $dbh->do($statement) or die
$dbh->errstr;
$rows = $dbh->do($statement, attr) or die
$dbh->errstr;
$rows = $dbh->do($statement, attr, @bind_values) or
die ...
Prepare and execute a single statement. Returns the
number of rows affected or "undef" on error. A return
value of "-1" means the number of rows is not known,
not applicable, or not available.
This method is typically most useful for non-"SELECT"
statements that either cannot be prepared in advance
(due to a limitation of the driver) or do not need to
be executed repeatedly. It should not be used for
"SELECT" statements because it does not return a
statement handle (so you can't fetch any data).
The default "do" method is logically similar to:

sub do {
my($dbh, $statement, $attr, @bind_values) = @_;
my $sth = $dbh->prepare($statement, $attr) or
return undef;
$sth->execute(@bind_values) or return undef;
my $rows = $sth->rows;
($rows == 0) ? "0E0" : $rows; # always return
true if no error
}
For example:

my $rows_deleted = $dbh->do(q{
DELETE FROM table
WHERE status = ?
}, undef, 'DONE') or die $dbh->errstr;
Using placeholders and @bind_values with the "do"
method can be useful because it avoids the need to
correctly quote any variables in the $statement. But
if you'll be executing the statement many times then
it's more efficient to "prepare" it once and call
"execute" many times instead.
The "q{...}" style quoting used in this example avoids
clashing with quotes that may be used in the SQL
statement. Use the double-quote-like "qq{...}" opera
tor if you want to interpolate variables into the
string. See "Quote and Quote-like Operators" in per
lop for more details.
"selectrow_array"
@row_ary = $dbh->selectrow_array($statement);
@row_ary = $dbh->selectrow_array($statement, attr);
@row_ary = $dbh->selectrow_array($statement, attr,
@bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_array" into a single call. If called in a
list context, it returns the first row of data from
the statement. The $statement parameter can be a pre
viously prepared statement handle, in which case the
"prepare" is skipped.
If any method fails, and "RaiseError" is not set,
"selectrow_array" will return an empty list.
If called in a scalar context for a statement handle
that has more than one column, it is undefined whether
the driver will return the value of the first column
or the last. So don't do that. Also, in a scalar con
text, an "undef" is returned if there are no more rows
or if an error occurred. That "undef" can't be distin
guished from an "undef" returned because the first
field value was NULL. For these reasons you should
exercise some caution if you use "selectrow_array" in
a scalar context.
"selectrow_arrayref"
$ary_ref = $dbh->selectrow_arrayref($statement);
$ary_ref = $dbh->selectrow_arrayref($statement, at
tr);
$ary_ref = $dbh->selectrow_arrayref($statement, at
tr, @bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_arrayref" into a single call. It returns the
first row of data from the statement. The $statement
parameter can be a previously prepared statement han
dle, in which case the "prepare" is skipped.
If any method fails, and "RaiseError" is not set,
"selectrow_array" will return undef.
"selectrow_hashref"
$hash_ref = $dbh->selectrow_hashref($statement);
$hash_ref = $dbh->selectrow_hashref($statement, at
tr);
$hash_ref = $dbh->selectrow_hashref($statement, at
tr, @bind_values);
This utility method combines "prepare", "execute" and
"fetchrow_hashref" into a single call. It returns the
first row of data from the statement. The $statement
parameter can be a previously prepared statement han
dle, in which case the "prepare" is skipped.
If any method fails, and "RaiseError" is not set,
"selectrow_hashref" will return undef.
"selectall_arrayref"
$ary_ref = $dbh->selectall_arrayref($statement);
$ary_ref = $dbh->selectall_arrayref($statement, at
tr);
$ary_ref = $dbh->selectall_arrayref($statement, at
tr, @bind_values);
This utility method combines "prepare", "execute" and
"fetchall_arrayref" into a single call. It returns a
reference to an array containing a reference to an
array for each row of data fetched.
The $statement parameter can be a previously prepared
statement handle, in which case the "prepare" is
skipped. This is recommended if the statement is going
to be executed many times.
If "RaiseError" is not set and any method except
"fetchall_arrayref" fails then "selectall_arrayref"
will return "undef"; if "fetchall_arrayref" fails then
it will return with whatever data has been fetched
thus far. You should check "$sth-">"err" afterwards
(or use the "RaiseError" attribute) to discover if the
data is complete or was truncated due to an error.
The "fetchall_arrayref" method called by "selec
tall_arrayref" supports a $max_rows parameter. You can
specify a value for $max_rows by including a
'"MaxRows"' attribute in attr.
The "fetchall_arrayref" method called by "selec
tall_arrayref" also supports a $slice parameter. You
can specify a value for $slice by including a
'"Slice"' or '"Columns"' attribute in attr. The only
difference between the two is that if "Slice" is not
defined and "Columns" is an array ref, then the array
is assumed to contain column index values (which count
from 1), rather than perl array index values. In
which case the array is copied and each value decre
mented before passing to "/fetchall_arrayref".
"selectall_hashref"
$hash_ref = $dbh->selectall_hashref($statement,
$key_field);
$hash_ref = $dbh->selectall_hashref($statement,
$key_field, attr);
$hash_ref = $dbh->selectall_hashref($statement,
$key_field, attr, @bind_values);
This utility method combines "prepare", "execute" and
"fetchall_hashref" into a single call. It returns a
reference to a hash containing one entry for each row.
The key for each row entry is specified by $key_field.
The value is a reference to a hash returned by
"fetchrow_hashref".
The $statement parameter can be a previously prepared
statement handle, in which case the "prepare" is
skipped. This is recommended if the statement is going
to be executed many times.
If any method except "fetchrow_hashref" fails, and
"RaiseError" is not set, "selectall_hashref" will
return "undef". If "fetchrow_hashref" fails and
"RaiseError" is not set, then it will return with
whatever data it has fetched thus far. $DBI::err
should be checked to catch that.
"selectcol_arrayref"
$ary_ref = $dbh->selectcol_arrayref($statement);
$ary_ref = $dbh->selectcol_arrayref($statement, at
tr);
$ary_ref = $dbh->selectcol_arrayref($statement, at
tr, @bind_values);
This utility method combines "prepare", "execute", and
fetching one column from all the rows, into a single
call. It returns a reference to an array containing
the values of the first column from each row.
The $statement parameter can be a previously prepared
statement handle, in which case the "prepare" is
skipped. This is recommended if the statement is going
to be executed many times.
If any method except "fetch" fails, and "RaiseError"
is not set, "selectcol_arrayref" will return "undef".
If "fetch" fails and "RaiseError" is not set, then it
will return with whatever data it has fetched thus
far. $DBI::err should be checked to catch that.
The "selectcol_arrayref" method defaults to pushing a
single column value (the first) from each row into the
result array. However, it can also push another col
umn, or even multiple columns per row, into the result
array. This behaviour can be specified via a
'"Columns"' attribute which must be a ref to an array
containing the column number or numbers to use. For
example:

# get array of id and name pairs:
my $ary_ref = $dbh->selectcol_arrayref("select id,
name from table", { Columns=>[1,2] });
my %hash = @$ary_ref; # build hash from key-value
pairs so $hash{$id} => name
"prepare"
$sth = $dbh->prepare($statement) or die
$dbh->errstr;
$sth = $dbh->prepare($statement, attr) or die
$dbh->errstr;
Prepares a single statement for later execution by the
database engine and returns a reference to a statement
handle object.
The returned statement handle can be used to get
attributes of the statement and invoke the "execute"
method. See "Statement Handle Methods".
Drivers for engines without the concept of preparing a
statement will typically just store the statement in
the returned handle and process it when "$sth-">"exe
cute" is called. Such drivers are unlikely to give
much useful information about the statement, such as
"$sth-">"{NUM_OF_FIELDS}", until after "$sth-">"exe
cute" has been called. Portable applications should
take this into account.
In general, DBI drivers do not parse the contents of
the statement (other than simply counting any "Place
holders"). The statement is passed directly to the
database engine, sometimes known as pass-thru mode.
This has advantages and disadvantages. On the plus
side, you can access all the functionality of the
engine being used. On the downside, you're limited if
you're using a simple engine, and you need to take
extra care if writing applications intended to be
portable between engines.
Portable applications should not assume that a new
statement can be prepared and/or executed while still
fetching results from a previous statement.
Some command-line SQL tools use statement terminators,
like a semicolon, to indicate the end of a statement.
Such terminators should not normally be used with the
DBI.
"prepare_cached"
$sth = $dbh->prepare_cached($statement)
$sth = $dbh->prepare_cached($statement, attr)
$sth = $dbh->prepare_cached($statement, attr, $al
low_active)
Like "prepare" except that the statement handle
returned will be stored in a hash associated with the
$dbh. If another call is made to "prepare_cached" with
the same $statement and %attr values, then the corre
sponding cached $sth will be returned without contact
ing the database server.
Here are some examples of "prepare_cached":

sub insert_hash {
my ($table, $field_values) = @_;
my @fields = sort keys %$field_values; # sort re
quired
my @values = @{$field_values}{@fields};
my $sql = sprintf "insert into %s (%s) values
(%s)",
$table, join(",", @fields), join(",",
("?")x@fields);
my $sth = $dbh->prepare_cached($sql);
return $sth->execute(@values);
}
sub search_hash {
my ($table, $field_values) = @_;
my @fields = sort keys %$field_values; # sort re
quired
my @values = @{$field_values}{@fields};
my $qualifier = "";
$qualifier = "where ".join(" and ", map { "$_=?" }
@fields) if @fields;
$sth = $dbh->prepare_cached("SELECT * FROM $table
$qualifier");
return $dbh->selectall_arrayref($sth, {}, @val
ues);
}
Caveat emptor: This caching can be useful in some applications, but it can also cause problems and
should be used with care. Here is a contrived case
where caching would cause a significant problem:

my $sth = $dbh->prepare_cached('SELECT * FROM foo
WHERE bar=?');
$sth->execute($bar);
while (my $data = $sth->fetchrow_hashref) {
my $sth2 = $dbh->prepare_cached('SELECT * FROM foo
WHERE bar=?');
$sth2->execute($data->{bar});
while (my $data2 = $sth2->fetchrow_arrayref) {
do_stuff(...);
}
}
In this example, since both handles are preparing the
exact same statement, $sth2 will not be its own state
ment handle, but a duplicate of $sth returned from the
cache. The results will certainly not be what you
expect. Typically the the inner fetch loop will work
normally, fetching all the records and terminating
when there are no more, but now $sth is the same as
$sth2 the outer fetch loop will also terminate.
The $allow_active parameter lets you adjust DBI's
behavior when prepare_cached is returning a statement
handle that is still active. There are three set
tings:

0: A warning will be generated, and "finish" will
be called on the statement handle before it is
returned. This is the default behavior if
$allow_active is not passed.
1: "finish" will be called on the statement han
dle, but the warning is suppressed.
2: DBI will not touch the statement handle before
returning it. You will need to check
"$sth-">"{Active}" on the returned statement han
dle and deal with it in your own code.
Because the cache used by prepare_cached() is keyed by all the parameters, including any attributes passed,
you can also avoid this issue by doing something like:

my $sth = $dbh->prepare_cached("...", { dbi_dummy =>
__FILE__.__LINE__ });
which will ensure that prepare_cached only returns
statements cached by that line of code in that source
file.
"commit"
$rc = $dbh->commit or die $dbh->errstr;
Commit (make permanent) the most recent series of
database changes if the database supports transactions
and AutoCommit is off.
If "AutoCommit" is on, then calling "commit" will
issue a "commit ineffective with AutoCommit" warning.
See also "Transactions" in the "FURTHER INFORMATION"
section below.
"rollback"
$rc = $dbh->rollback or die $dbh->errstr;
Rollback (undo) the most recent series of uncommitted
database changes if the database supports transactions
and AutoCommit is off.
If "AutoCommit" is on, then calling "rollback" will
issue a "rollback ineffective with AutoCommit" warn
ing.
See also "Transactions" in the "FURTHER INFORMATION"
section below.
"begin_work"
$rc = $dbh->begin_work or die $dbh->errstr;
Enable transactions (by turning "AutoCommit" off)
until the next call to "commit" or "rollback". After
the next "commit" or "rollback", "AutoCommit" will
automatically be turned on again.
If "AutoCommit" is already off when "begin_work" is
called then it does nothing except return an error. If
the driver does not support transactions then when
"begin_work" attempts to set "AutoCommit" off the
driver will trigger a fatal error.
See also "Transactions" in the "FURTHER INFORMATION"
section below.
"disconnect"
$rc = $dbh->disconnect or warn $dbh->errstr;
Disconnects the database from the database handle.
"disconnect" is typically only used before exiting the
program. The handle is of little use after disconnect
ing.
The transaction behavior of the "disconnect" method
is, sadly, undefined. Some database systems (such as
Oracle and Ingres) will automatically commit any out
standing changes, but others (such as Informix) will
rollback any outstanding changes. Applications not
using "AutoCommit" should explicitly call "commit" or
"rollback" before calling "disconnect".
The database is automatically disconnected by the
"DESTROY" method if still connected when there are no
longer any references to the handle. The "DESTROY"
method for each driver should implicitly call "roll
back" to undo any uncommitted changes. This is vital
behavior to ensure that incomplete transactions don't
get committed simply because Perl calls "DESTROY" on
every object before exiting. Also, do not rely on the
order of object destruction during "global destruc
tion", as it is undefined.
Generally, if you want your changes to be commited or
rolled back when you disconnect, then you should
explicitly call "commit" or "rollback" before discon
necting.
If you disconnect from a database while you still have
active statement handles (e.g., SELECT statement han
dles that may have more data to fetch), you will get a
warning. The warning may indicate that a fetch loop
terminated early, perhaps due to an uncaught error.
To avoid the warning call the "finish" method on the
active handles.
"ping"
$rc = $dbh->ping;
Attempts to determine, in a reasonably efficient way,
if the database server is still running and the con
nection to it is still working. Individual drivers
should implement this function in the most suitable
manner for their database engine.
The current default implementation always returns true without actually doing anything. Actually, it returns
""0 but true"" which is true but zero. That way you
can tell if the return value is genuine or just the
default. Drivers should override this method with one
that does the right thing for their type of database.
Few applications would have direct use for this
method. See the specialized Apache::DBI module for one
example usage.
"get_info" NEW
Warning: This method is experimental and may change.

$value = $dbh->get_info( $info_type );
Returns information about the implementation, i.e.
driver and data source capabilities, restrictions etc.
It returns "undef" for unknown or unimplemented infor
mation types. For example:

$database_version = $dbh->get_info( 18 ); #
SQL_DBMS_VER
$max_select_tables = $dbh->get_info( 106 ); #
SQL_MAXIMUM_TABLES_IN_SELECT
See "Standards Reference Information" for more
detailed information about the information types and
their meanings and possible return values.
The DBI curently doesn't provide a name to number map
ping for the information type codes or the results.
Applications are expected to use the integer values
directly, with the name in a comment, or define their
own named values using something like the constant
pragma.
Because some DBI methods make use of get_info(), drivers are strongly encouraged to support at least
the following very minimal set of information types to
ensure the DBI itself works properly:

Type Name Example A Exam
ple B
---- -------------------------- -----------
-----------
17 SQL_DBMS_NAME 'ACCESS' 'Ora
cle'
18 SQL_DBMS_VER '03.50.0000'
'08.01.0721'
29 SQL_IDENTIFIER_QUOTE_CHAR '`' '"'
41 SQL_CATALOG_NAME_SEPARATOR '.' '@'
114 SQL_CATALOG_LOCATION 1 2
"table_info" NEW
Warning: This method is experimental and may change.

$sth = $dbh->table_info( $catalog, $schema, $table,
$type );
$sth = $dbh->table_info( $catalog, $schema, $table,
$type, attr );
$sth = $dbh->table_info( attr ); # old style
Returns an active statement handle that can be used to
fetch information about tables and views that exist in
the database.
The old style interface passes all the parameters as a
reference to an attribute hash with some or all of the
following attributes:

%attr = (
TABLE_CAT => $catalog # String value of the
catalog name
, TABLE_SCHEM => $schema # String value of the
schema name
, TABLE_NAME => $table # String value of the
table name
, TABLE_TYPE => $type # String value of the
table type(s)
);
The old style interface is deprecated and will be
removed in a future version.
The support for the selection criteria is driver spe
cific. If the driver doesn't support one or more of
them then you may get back more than you asked for and
can do the filtering yourself.
The arguments $catalog, $schema and $table may accept
search patterns according to the database/driver, for
example: $table = '%FOO%'; Remember that the under
score character ('"_"') is a search pattern that means
match any character, so 'FOO_%' is the same as 'FOO%'
and 'FOO_BAR%' will match names like 'FOO1BAR'.
The value of $type is a comma-separated list of one or
more types of tables to be returned in the result set.
Each value may optionally be quoted, e.g.:

$type = "TABLE";
$type = "'TABLE','VIEW'";
In addition the following special cases may also be
supported by some drivers:
· If the value of $catalog is '%' and $schema and
$table name are empty strings, the result set contains
a list of catalog names. For example:
$sth = $dbh->table_info('%', '', '');
· If the value of $schema is '%' and $catalog and
$table are empty strings, the result set contains a
list of schema names.
· If the value of $type is '%' and $catalog, $schema,
and $table are all empty strings, the result set con
tains a list of table types.
The statement handle returned has at least the follow
ing fields in the order show below. Other fields,
after these, may also be present.
TABLE_CAT: Table catalog identifier. This field is NULL ("undef") if not applicable to the data source,
which is usually the case. This field is empty if not
applicable to the table.
TABLE_SCHEM: The name of the schema containing the TABLE_NAME value. This field is NULL ("undef") if not
applicable to data source, and empty if not applicable
to the table.
TABLE_NAME: Name of the table (or view, synonym, etc).
TABLE_TYPE: One of the following: "TABLE", "VIEW", "SYSTEM TABLE", "GLOBAL TEMPORARY", "LOCAL TEMPORARY",
"ALIAS", "SYNONYM" or a type identifier that is spe
cific to the data source.
REMARKS: A description of the table. May be NULL
("undef").
Note that "table_info" might not return records for
all tables. Applications can use any valid table
regardless of whether it's returned by "table_info".
See also "tables", "Catalog Methods" and "Standards
Reference Information".
"column_info" NEW
Warning: This method is experimental and may change.

$sth = $dbh->column_info( $catalog, $schema, $table,
$column );
Returns an active statement handle that can be used to
fetch information about columns in specified tables.
The arguments $schema, $table and $column may accept
search patterns according to the database/driver, for
example: $table = '%FOO%';
Note: The support for the selection criteria is driver
specific. If the driver doesn't support one or more of
them then you may get back more than you asked for and
can do the filtering yourself.
The statement handle returned has at least the follow
ing fields in the order shown below. Other fields,
after these, may also be present.
TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not applicable to the data source, which
is often the case. This field is empty if not appli
cable to the table.
TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if not applicable to the data source,
and empty if not applicable to the table.
TABLE_NAME: The table identifier. Note: A driver may provide column metadata not only for base tables, but
also for derived objects like SYNONYMS etc.
COLUMN_NAME: The column identifier.
DATA_TYPE: The concise data type code.
TYPE_NAME: A data source dependent data type name.
COLUMN_SIZE: The column size. This is the maximum length in characters for character data types, the
number of digits or bits for numeric data types or the
length in the representation of temporal types. See
the relevant specifications for detailed information.
BUFFER_LENGTH: The length in bytes of transferred data.
DECIMAL_DIGITS: The total number of significant digits to the right of the decimal point.
NUM_PREC_RADIX: The radix for numeric precision. The value is 10 or 2 for numeric data types and NULL
("undef") if not applicable.
NULLABLE: Indicates if a column can accept NULLs. The following values are defined:

SQL_NO_NULLS 0
SQL_NULLABLE 1
SQL_NULLABLE_UNKNOWN 2
REMARKS: A description of the column.
COLUMN_DEF: The default value of the column.
SQL_DATA_TYPE: The SQL data type.
SQL_DATETIME_SUB: The subtype code for datetime and interval data types.
CHAR_OCTET_LENGTH: The maximum length in bytes of a character or binary data type column.
ORDINAL_POSITION: The column sequence number (starting with 1).
IS_NULLABLE: Indicates if the column can accept NULLs. Possible values are: 'NO', 'YES' and ''.
SQL/CLI defines the following additional columns:

CHAR_SET_CAT
CHAR_SET_SCHEM
CHAR_SET_NAME
COLLATION_CAT
COLLATION_SCHEM
COLLATION_NAME
UDT_CAT
UDT_SCHEM
UDT_NAME
DOMAIN_CAT
DOMAIN_SCHEM
DOMAIN_NAME
SCOPE_CAT
SCOPE_SCHEM
SCOPE_NAME
MAX_CARDINALITY
DTD_IDENTIFIER
IS_SELF_REF
Drivers capable of supplying any of those values
should do so in the corresponding column and supply
undef values for the others.
Drivers wishing to provide extra database/driver spe
cific information should do so in extra columns beyond
all those listed above, and use lowercase field names
with the driver-specific prefix (i.e., 'ora_...').
Applications accessing such fields should do so by
name and not by column number.
The result set is ordered by TABLE_CAT, TABLE_SCHEM,
TABLE_NAME and ORDINAL_POSITION.
Note: There is some overlap with statement attributes
(in perl) and SQLDescribeCol (in ODBC). However, SQL
Columns provides more metadata.
See also "Catalog Methods" and "Standards Reference
Information".
"primary_key_info" NEW
Warning: This method is experimental and may change.

$sth = $dbh->primary_key_info( $catalog, $schema,
$table );
Returns an active statement handle that can be used to
fetch information about columns that make up the pri
mary key for a table. The arguments don't accept
search patterns (unlike table_info()).
For example:

$sth = $dbh->primary_key_info( undef, $user, 'foo'
);
$data = $sth->fetchall_arrayref;
Note: The support for the selection criteria, such as
$catalog, is driver specific. If the driver doesn't
support catalogs and/or schemas, it may ignore these
criteria.
The statement handle returned has at least the follow
ing fields in the order shown below. Other fields,
after these, may also be present.
TABLE_CAT: The catalog identifier. This field is NULL ("undef") if not applicable to the data source, which
is often the case. This field is empty if not appli
cable to the table.
TABLE_SCHEM: The schema identifier. This field is NULL ("undef") if not applicable to the data source,
and empty if not applicable to the table.
TABLE_NAME: The table identifier.
COLUMN_NAME: The column identifier.
KEY_SEQ: The column sequence number (starting with 1). Note: This field is named ORDINAL_POSITION in SQL/CLI.
PK_NAME: The primary key constraint identifier. This field is NULL ("undef") if not applicable to the data
source.
See also "Catalog Methods" and "Standards Reference
Information".
"primary_key" NEW
Warning: This method is experimental and may change.

@key_column_names = $dbh->primary_key( $catalog,
$schema, $table );
Simple interface to the primary_key_info() method. Returns a list of the column names that comprise the
primary key of the specified table. The list is in
primary key column sequence order.
"foreign_key_info" NEW
Warning: This method is experimental and may change.

$sth = $dbh->foreign_key_info( $pk_catalog,
$pk_schema, $pk_table
, $fk_catalog,
$fk_schema, $fk_table );
Returns an active statement handle that can be used to
fetch information about foreign keys in and/or refer
encing the specified table(s). The arguments don't
accept search patterns (unlike table_info()).
$pk_catalog, $pk_schema, $pk_table identify the pri
mary (unique) key table (PKT).
$fk_catalog, $fk_schema, $fk_table identify the for
eign key table (FKT).
If both PKT and FKT are given, the function returns
the foreign key, if any, in table FKT that refers to
the primary (unique) key of table PKT. (Note: In
SQL/CLI, the result is implementation-defined.)
If only PKT is given, then the result set contains the
primary key of that table and all foreign keys that
refer to it.
If only FKT is given, then the result set contains all
foreign keys in that table and the primary keys to
which they refer. (Note: In SQL/CLI, the result
includes unique keys too.)
For example:

$sth = $dbh->foreign_key_info( undef, $user, 'mas
ter');
$sth = $dbh->foreign_key_info( undef, undef, undef
, undef, $user, 'detail');
$sth = $dbh->foreign_key_info( undef, $user, 'mas
ter', undef, $user, 'detail');
Note: The support for the selection criteria, such as
$catalog, is driver specific. If the driver doesn't
support catalogs and/or schemas, it may ignore these
criteria.
The statement handle returned has the following fields
in the order shown below. Because ODBC never includes
unique keys, they define different columns in the
result set than SQL/CLI. SQL/CLI column names are
shown in parentheses.
PKTABLE_CAT ( UK_TABLE_CAT ): The primary (unique) key table catalog identifier. This field is
NULL ("undef") if not applicable to the data source,
which is often the case. This field is empty if not
applicable to the table.
PKTABLE_SCHEM ( UK_TABLE_SCHEM ): The primary (unique) key table schema identifier. This field is
NULL ("undef") if not applicable to the data source,
and empty if not applicable to the table.
PKTABLE_NAME ( UK_TABLE_NAME ): The primary (unique) key table identifier.
PKCOLUMN_NAME (UK_COLUMN_NAME ): The primary (unique) key column identifier.
FKTABLE_CAT ( FK_TABLE_CAT ): The foreign key table catalog identifier. This field is NULL
("undef") if not applicable to the data source, which
is often the case. This field is empty if not appli
cable to the table.
FKTABLE_SCHEM ( FK_TABLE_SCHEM ): The foreign key table schema identifier. This field is NULL ("undef")
if not applicable to the data source, and empty if not
applicable to the table.
FKTABLE_NAME ( FK_TABLE_NAME ): The foreign key table identifier.
FKCOLUMN_NAME ( FK_COLUMN_NAME ): The foreign key column identifier.
KEY_SEQ ( ORDINAL_POSITION ): The column sequence number (starting with 1).
UPDATE_RULE ( UPDATE_RULE ): The referential action for the UPDATE rule. The following codes are
defined:

CASCADE 0
RESTRICT 1
SET NULL 2
NO ACTION 3
SET DEFAULT 4
DELETE_RULE ( DELETE_RULE ): The referential action for the DELETE rule. The codes are the same as
for UPDATE_RULE.
FK_NAME ( FK_NAME ): The foreign key name.
PK_NAME ( UK_NAME ): The primary (unique) key name.
DEFERRABILITY ( DEFERABILITY ): The deferrabil ity of the foreign key constraint. The following
codes are defined:

INITIALLY DEFERRED 5
INITIALLY IMMEDIATE 6
NOT DEFERRABLE 7

( UNIQUE_OR_PRIMARY ): This column is
necessary if a driver includes all candidate (i.e.
primary and alternate) keys in the result set (as
specified by SQL/CLI). The value of this column is
UNIQUE if the foreign key references an alternate key
and PRIMARY if the foreign key references a primary
key, or it may be undefined if the driver doesn't have
access to the information.
See also "Catalog Methods" and "Standards Reference
Information".
"tables" NEW
Warning: This method is experimental and may change.

@names = $dbh->tables( $catalog, $schema, $table,
$type );
@names = $dbh->tables; # deprecated
Simple interface to table_info(). Returns a list of matching table names, possibly including a cata
log/schema prefix.
See "table_info" for a description of the parameters.
If "$dbh-">"get_info(29)" returns true (29 is
SQL_IDENTIFIER_QUOTE_CHAR) then the table names are
constructed and quoted by "quote_identifier" to ensure
they are usable even if they contain whitespace or
reserved words etc.
"type_info_all"
Warning: This method is experimental and may change.

$type_info_all = $dbh->type_info_all;
Returns a reference to an array which holds informa
tion about each data type variant supported by the
database and driver. The array and its contents should
be treated as read-only.
The first item is a reference to an 'index' hash of
"Name ="> "Index" pairs. The items following that are
references to arrays, one per supported data type
variant. The leading index hash defines the names and
order of the fields within the arrays that follow it.
For example:

$type_info_all = [
{ TYPE_NAME => 0,
DATA_TYPE => 1,
COLUMN_SIZE => 2, # was PRECISION
originally
LITERAL_PREFIX => 3,
LITERAL_SUFFIX => 4,
CREATE_PARAMS => 5,
NULLABLE => 6,
CASE_SENSITIVE => 7,
SEARCHABLE => 8,
UNSIGNED_ATTRIBUTE=> 9,
FIXED_PREC_SCALE => 10, # was MONEY origi
nally
AUTO_UNIQUE_VALUE => 11, # was AUTO_INCRE
MENT originally
LOCAL_TYPE_NAME => 12,
MINIMUM_SCALE => 13,
MAXIMUM_SCALE => 14,
NUM_PREC_RADIX => 15,
},
[ 'VARCHAR', SQL_VARCHAR,
undef, "'","'", undef,0, 1,1,0,0,0,un
def,1,255, undef
],
[ 'INTEGER', SQL_INTEGER,
undef, "", "", undef,0, 0,1,0,0,0,undef,0,
0, 10
],
];
Note that more than one row may have the same value in
the "DATA_TYPE" field if there are different ways to
spell the type name and/or there are variants of the
type with different attributes (e.g., with and without
"AUTO_UNIQUE_VALUE" set, with and without
"UNSIGNED_ATTRIBUTE", etc).
The rows are ordered by "DATA_TYPE" first and then by
how closely each type maps to the corresponding ODBC
SQL data type, closest first.
The meaning of the fields is described in the documen
tation for the "type_info" method. The index values
shown above (e.g., "NULLABLE ="> 6) are for illustra
tion only. Drivers may define the fields with a dif
ferent order.
This method is not normally used directly. The
"type_info" method provides a more useful interface to
the data.
Even though an 'index' hash is provided, all the field
names in the index hash defined above will always have
the index values defined above. This is defined
behaviour so that you don't need to rely on the index
hash, which is handy because the lettercase of the
keys is not defined. It is usually uppercase, as show
here, but drivers are free to return names with any
lettercase. Drivers are also free to return extra
driver-specific columns of information - though it's
recommended that they start at column index 50 to
leave room for expansion of the DBI/ODBC specifica
tion.
"type_info"
Warning: This method is experimental and may change.

@type_info = $dbh->type_info($data_type);
Returns a list of hash references holding information
about one or more variants of $data_type. The list is
ordered by "DATA_TYPE" first and then by how closely
each type maps to the corresponding ODBC SQL data
type, closest first. If called in a scalar context
then only the first (best) element is returned.
If $data_type is undefined or "SQL_ALL_TYPES", then
the list will contain hashes for all data type vari
ants supported by the database and driver.
If $data_type is an array reference then "type_info"
returns the information for the first type in the
array that has any matches.
The keys of the hash follow the same letter case con
ventions as the rest of the DBI (see "Naming Conven
tions and Name Space"). The following items should
exist:
TYPE_NAME (string)
Data type name for use in CREATE TABLE statements
etc.
DATA_TYPE (integer)
SQL data type number.
COLUMN_SIZE (integer)
For numeric types, this is either the total number
of digits (if the NUM_PREC_RADIX value is 10) or
the total number of bits allowed in the column (if
NUM_PREC_RADIX is 2).
For string types, this is the maximum size of the
string in bytes.
For date and interval types, this is the maximum
number of characters needed to display the value.
LITERAL_PREFIX (string)
Characters used to prefix a literal. A typical
prefix is ""'"" for characters, or possibly ""0x""
for binary values passed as hexadecimal. NULL
("undef") is returned for data types for which
this is not applicable.
LITERAL_SUFFIX (string)
Characters used to suffix a literal. Typically
""'"" for characters. NULL ("undef") is returned
for data types where this is not applicable.
CREATE_PARAMS (string)
Parameter names for data type definition. For
example, "CREATE_PARAMS" for a "DECIMAL" would be
""precision,scale"" if the DECIMAL type should be
declared as "DECIMAL("precision,scale")" where precision and scale are integer values. For a "VARCHAR" it would be ""max length"". NULL
("undef") is returned for data types for which
this is not applicable.
NULLABLE (integer)
Indicates whether the data type accepts a NULL
value: 0 or an empty string = no, 1 = yes, 2 =
unknown.
CASE_SENSITIVE (boolean)
Indicates whether the data type is case sensitive
in collations and comparisons.
SEARCHABLE (integer)
Indicates how the data type can be used in a WHERE
clause, as follows:

0 - Cannot be used in a WHERE clause
1 - Only with a LIKE predicate
2 - All comparison operators except LIKE
3 - Can be used in a WHERE clause with any com
parison operator
UNSIGNED_ATTRIBUTE (boolean)
Indicates whether the data type is unsigned. NULL
("undef") is returned for data types for which
this is not applicable.
FIXED_PREC_SCALE (boolean)
Indicates whether the data type always has the
same precision and scale (such as a money type).
NULL ("undef") is returned for data types for
which this is not applicable.
AUTO_UNIQUE_VALUE (boolean)
Indicates whether a column of this data type is
automatically set to a unique value whenever a new
row is inserted. NULL ("undef") is returned for
data types for which this is not applicable.
LOCAL_TYPE_NAME (string)
Localized version of the "TYPE_NAME" for use in
dialog with users. NULL ("undef") is returned if
a localized name is not available (in which case
"TYPE_NAME" should be used).
MINIMUM_SCALE (integer)
The minimum scale of the data type. If a data type
has a fixed scale, then "MAXIMUM_SCALE" holds the
same value. NULL ("undef") is returned for data
types for which this is not applicable.
MAXIMUM_SCALE (integer)
The maximum scale of the data type. If a data type
has a fixed scale, then "MINIMUM_SCALE" holds the
same value. NULL ("undef") is returned for data
types for which this is not applicable.
SQL_DATA_TYPE (integer)
This column is the same as the "DATA_TYPE" column,
except for interval and datetime data types. For
interval and datetime data types, the
"SQL_DATA_TYPE" field will return "SQL_INTERVAL"
or "SQL_DATETIME", and the "SQL_DATETIME_SUB"
field below will return the subcode for the spe
cific interval or datetime data type. If this
field is NULL, then the driver does not support or
report on interval or date subtypes.
SQL_DATETIME_SUB (integer)
For interval or datetime data types, where the
"SQL_DATA_TYPE" field above is "SQL_INTERVAL" or
"SQL_DATETIME", this field will hold the subcode
for the specific interval or datetime data type.
Otherwise it will be NULL ("undef").
NUM_PREC_RADIX (integer)
The radix value of the data type. For approximate
numeric types, "NUM_PREC_RADIX" contains the value
2 and "COLUMN_SIZE" holds the number of bits. For
exact numeric types, "NUM_PREC_RADIX" contains the
value 10 and "COLUMN_SIZE" holds the number of
decimal digits. NULL ("undef") is returned either
for data types for which this is not applicable or
if the driver cannot report this information.
INTERVAL_PRECISION (integer)
The interval leading precision for interval types.
NULL is returned either for data types for which
this is not applicable or if the driver cannot
report this information.
For example, to find the type name for the fields in a
select statement you can do:

@names = map { scalar $dbh->type_in
fo($_)->{TYPE_NAME} } @{ $sth->{TYPE} }
Since DBI and ODBC drivers vary in how they map their
types into the ISO standard types you may need to
search for more than one type. Here's an example
looking for a usable type to store a date:

$my_date_type = $dbh->type_info( [ SQL_DATE,
SQL_TIMESTAMP ] );
Similarly, to more reliably find a type to store small
integers, you could use a list starting with
"SQL_SMALLINT", "SQL_INTEGER", "SQL_DECIMAL", etc.
See also "Standards Reference Information".
"quote"
$sql = $dbh->quote($value);
$sql = $dbh->quote($value, $data_type);
Quote a string literal for use as a literal value in
an SQL statement, by escaping any special characters
(such as quotation marks) contained within the string
and adding the required type of outer quotation marks.

$sql = sprintf "SELECT foo FROM bar WHERE baz = %s",
$dbh->quote("Don't");
For most database types, quote would return 'Don''t'
(including the outer quotation marks).
An undefined $value value will be returned as the
string "NULL" (without single quotation marks) to
match how NULLs are represented in SQL.
If $data_type is supplied, it is used to try to deter
mine the required quoting behavior by using the infor
mation returned by "type_info". As a special case,
the standard numeric types are optimized to return
$value without calling "type_info".
Quote will probably not be able to deal with all pos
sible input (such as binary data or data containing
newlines), and is not related in any way with escaping
or quoting shell meta-characters. There is no need to
quote values being used with "Placeholders and Bind
Values".
"quote_identifier"
$sql = $dbh->quote_identifier( $name );
$sql = $dbh->quote_identifier( $name1, $name2,
$name3, attr );
Quote an identifier (table name etc.) for use in an
SQL statement, by escaping any special characters
(such as double quotation marks) it contains and
adding the required type of outer quotation marks.
Undefined names are ignored and the remainder are
quoted and then joined together, typically with a dot
(".") character. For example:

$id = $dbh->quote_identifier( undef, 'Her schema',
'My table' );
would, for most database types, return "Her
schema"."My table" (including all the double quotation
marks).
If three names are supplied then the first is assumed
to be a catalog name and special rules may be applied
based on what "get_info" returns for SQL_CATA
LOG_NAME_SEPARATOR (41) and SQL_CATALOG_LOCATION
(114). For example, for Oracle:

$id = $dbh->quote_identifier( 'link', 'schema', 'ta
ble' );
would return "schema"."table"@"link".
Database Handle Attributes
This section describes attributes specific to database
handles.
Changes to these database handle attributes do not affect
any other existing or future database handles.
Attempting to set or get the value of an unknown attribute
is fatal, except for private driver-specific attributes
(which all have names starting with a lowercase letter).
Example:

$h->{AutoCommit} = ...; # set/write
... = $h->{AutoCommit}; # get/read
"AutoCommit" (boolean)
If true, then database changes cannot be rolled-back
(undone). If false, then database changes automati
cally occur within a "transaction", which must either
be committed or rolled back using the "commit" or
"rollback" methods.
Drivers should always default to "AutoCommit" mode (an
unfortunate choice largely forced on the DBI by ODBC
and JDBC conventions.)
Attempting to set "AutoCommit" to an unsupported value
is a fatal error. This is an important feature of the
DBI. Applications that need full transaction behavior
can set "$dbh-">"{AutoCommit} = 0" (or set "AutoCom
mit" to 0 via "connect") without having to check that
the value was assigned successfully.
For the purposes of this description, we can divide
databases into three categories:

Databases which don't support transactions at all.
Databases in which a transaction is always active.
Databases in which a transaction must be explicitly
started (C<'BEGIN WORK'>).
* Databases which don't support transactions at all
For these databases, attempting to turn "AutoCommit"
off is a fatal error. "commit" and "rollback" both
issue warnings about being ineffective while "AutoCom
mit" is in effect.
* Databases in which a transaction is always active
These are typically mainstream commercial relational
databases with "ANSI standard" transaction behavior.
If "AutoCommit" is off, then changes to the database
won't have any lasting effect unless "commit" is
called (but see also "disconnect"). If "rollback" is
called then any changes since the last commit are
undone.
If "AutoCommit" is on, then the effect is the same as
if the DBI called "commit" automatically after every
successful database operation. So calling "commit" or
"rollback" explicitly while "AutoCommit" is on would
be ineffective because the changes would have already
been commited.
Changing "AutoCommit" from off to on will trigger a
"commit".
For databases which don't support a specific auto-com
mit mode, the driver has to commit each statement
automatically using an explicit "COMMIT" after it com
pletes successfully (and roll it back using an
explicit "ROLLBACK" if it fails). The error informa
tion reported to the application will correspond to
the statement which was executed, unless it succeeded
and the commit or rollback failed.
* Databases in which a transaction must be explicitly started
For these databases, the intention is to have them act
like databases in which a transaction is always active
(as described above).
To do this, the driver will automatically begin an
explicit transaction when "AutoCommit" is turned off,
or after a "commit" or "rollback" (or when the appli
cation issues the next database operation after one of
those events).
In this way, the application does not have to treat
these databases as a special case.
See "commit", "disconnect" and "Transactions" for
other important notes about transactions.
"Driver" (handle)
Holds the handle of the parent driver. The only recom
mended use for this is to find the name of the driver
using:

$dbh->{Driver}->{Name}
"Name" (string)
Holds the "name" of the database. Usually (and recom
mended to be) the same as the ""dbi:DriverName:...""
string used to connect to the database, but with the
leading ""dbi:DriverName:"" removed.
"Statement" (string, read-only)
Returns the statement string passed to the most recent
"prepare" method called in this database handle, even
if that method failed. This is especially useful where
"RaiseError" is enabled and the exception handler
checks $@ and sees that a 'prepare' method call
failed.
"RowCacheSize" (integer)
A hint to the driver indicating the size of the local
row cache that the application would like the driver
to use for future "SELECT" statements. If a row cache
is not implemented, then setting "RowCacheSize" is
ignored and getting the value returns "undef".
Some "RowCacheSize" values have special meaning, as
follows:

0 - Automatically determine a reasonable cache size
for each C<SELECT>
1 - Disable the local row cache
>1 - Cache this many rows
<0 - Cache as many rows that will fit into this much
memory for each C<SELECT>.
Note that large cache sizes may require a very large
amount of memory (cached rows * maximum size of row). Also, a large cache will cause a longer delay not only
for the first fetch, but also whenever the cache needs
refilling.
See also the "RowsInCache" statement handle attribute.

DBI STATEMENT HANDLE OBJECTS

This section lists the methods and attributes associated
with DBI statement handles.

Statement Handle Methods

The DBI defines the following methods for use on DBI
statement handles:

"bind_param"
$rc = $sth->bind_param($p_num, $bind_value) or die
$sth->errstr;
$rv = $sth->bind_param($p_num, $bind_value, attr)
or ...
$rv = $sth->bind_param($p_num, $bind_value,
$bind_type) or ...
The "bind_param" method can be used to bind a value
with a placeholder embedded in the prepared statement.
Placeholders are indicated with question mark charac
ter ("?"). For example:

$dbh->{RaiseError} = 1; # save having to
check each method call
$sth = $dbh->prepare("SELECT name, age FROM people
WHERE name LIKE ?");
$sth->bind_param(1, "John%"); # placeholders are
numbered from 1
$sth->execute;
DBI::dump_results($sth);
Note that the "?" is not enclosed in quotation marks,
even when the placeholder represents a string. Some
drivers also allow placeholders like ":"name and ":"n
(e.g., ":1", ":2", and so on) in addition to "?", but
their use is not portable. Undefined bind values or
"undef" can be used to indicate null values.
Some drivers do not support placeholders.
With most drivers, placeholders can't be used for any
element of a statement that would prevent the database
server from validating the statement and creating a
query execution plan for it. For example:

"SELECT name, age FROM ?" # wrong (will
probably fail)
"SELECT name, ? FROM people" # wrong (but may
not 'fail')
Also, placeholders can only represent single scalar
values. For example, the following statement won't
work as expected for more than one value:

"SELECT name, age FROM people WHERE name IN (?)"
# wrong
Data Types for Placeholders
The "attr" parameter can be used to hint at the data
type the placeholder should have. Typically, the
driver is only interested in knowing if the place
holder should be bound as a number or a string.

$sth->bind_param(1, $value, { TYPE => SQL_INTEGER
});
As a short-cut for this common case, the data type can
be passed directly, in place of the "attr" hash ref
erence. This example is equivalent to the one above:

$sth->bind_param(1, $value, SQL_INTEGER);
The "TYPE" value indicates the standard
(non-driver-specific) type for this parameter. To
specify the driver-specific type, the driver may sup
port a driver-specific attribute, such as "{ ora_type
=">" 97 }". The data type for a placeholder cannot be
changed after the first "bind_param" call. However, it
can be left unspecified, in which case it defaults to
the previous value.
The SQL_INTEGER and other related constants can be
imported using

use DBI qw(:sql_types);
See "DBI Constants" for more information.
Perl only has string and number scalar data types. All
database types that aren't numbers are bound as
strings and must be in a format the database will
understand.
As an alternative to specifying the data type in the
"bind_param" call, you can let the driver pass the
value as the default type ("VARCHAR"). You can then
use an SQL function to convert the type within the
statement. For example:

INSERT INTO price(code, price) VALUES (?, CON
VERT(MONEY,?))
The "CONVERT" function used here is just an example.
The actual function and syntax will vary between dif
ferent databases and is non-portable.
See also "Placeholders and Bind Values" for more
information.
"bind_param_inout"
$rc = $sth->bind_param_inout($p_num, ind_value,
$max_len) or die $sth->errstr;
$rv = $sth->bind_param_inout($p_num, ind_value,
$max_len, attr) or ...
$rv = $sth->bind_param_inout($p_num, ind_value,
$max_len, $bind_type) or ...
This method acts like "bind_param", but also enables
values to be updated by the statement. The statement
is typically a call to a stored procedure. The
$bind_value must be passed as a reference to the
actual value to be used.
Note that unlike "bind_param", the $bind_value vari
able is not read when "bind_param_inout" is called.
Instead, the value in the variable is read at the time
"execute" is called.
The additional $max_len parameter specifies the mini
mum amount of memory to allocate to $bind_value for
the new value. If the value returned from the database
is too big to fit, then the execution should fail. If
unsure what value to use, pick a generous length,
i.e., a length larger than the longest value that
would ever be returned. The only cost of using a
larger value than needed is wasted memory.
It is expected that few drivers will support this
method. The only driver currently known to do so is
DBD::Oracle (DBD::ODBC may support it in a future
release). Therefore it should not be used for database
independent applications.
Undefined values or "undef" are used to indicate null
values. See also "Placeholders and Bind Values" for
more information.
"bind_param_array"
$rc = $sth->bind_param_array($p_num, $ar
ray_ref_or_value)
$rc = $sth->bind_param_array($p_num, $ar
ray_ref_or_value, attr)
$rc = $sth->bind_param_array($p_num, $ar
ray_ref_or_value, $bind_type)
The "bind_param_array" method is used to bind an array
of values to a placeholder embedded in the prepared
statement which is to be executed with "exe
cute_array". For example:

$dbh->{RaiseError} = 1; # save having to
check each method call
$sth = $dbh->prepare("INSERT INTO people(first_name,
last_name) VALUES(?, ?)");
$sth->bind_param_array(1, [ 'John', 'Mary', 'Tim'
]);
$sth->bind_param_array(2, [ 'Booth', 'Todd', 'Robin
son' ]);
my @tuple_status;
$sth->execute_array(@tuple_status);
The %attr argument is the same as defined for
"bind_param". Refer to "bind_param" for general
details on using placeholders.
Each array bound to the statement must have the same
number of elements. Some drivers may define a method
attribute to relax this safety check.
Scalar values, including "undef", may also be bound by
"bind_param_array". In which case the same value will
be used for each "execute" call. Driver-specific
implementations may behave differently, e.g., when
binding to a stored procedure call, some databases
permit mixing scalars and arrays as arguments.
The default implementation provided by DBI (for
drivers that have not implemented array binding) is to
iteratively "execute" for each parameter tuple pro
vided in the bound arrays. Drivers may provide more
optimized implementations using whatever bulk opera
tion support the database API provides. The default
driver behaviour should match the default DBI
behaviour, but always consult your driver documenta
tion as there may be driver specific issues to con
sider.
Note that the default implementation currently only
supports non-data returning statements. Also,
"bind_param_array" and "bind_param" cannot be mixed in
the same statement execution, and "bind_param_array"
must be used with "execute_array"; using
"bind_param_array" will have no effect for "execute".
"execute"
$rv = $sth->execute or die
$sth->errstr;
$rv = $sth->execute(@bind_values) or die
$sth->errstr;
Perform whatever processing is necessary to execute
the prepared statement. An "undef" is returned if an
error occurs. A successful "execute" always returns
true regardless of the number of rows affected, even
if it's zero (see below). It is always important to
check the return status of "execute" (and most other
DBI methods) for errors.
For a non-"SELECT" statement, "execute" returns the
number of rows affected, if known. If no rows were
affected, then "execute" returns "0E0", which Perl
will treat as 0 but will regard as true. Note that it
is not an error for no rows to be affected by a state
ment. If the number of rows affected is not known,
then "execute" returns -1.
For "SELECT" statements, execute simply "starts" the
query within the database engine. Use one of the fetch
methods to retreive the data after calling "execute".
The "execute" method does not return the number of
rows that will be returned by the query (because most
databases can't tell in advance), it simply returns a
true value.
If any arguments are given, then "execute" will effec
tively call "bind_param" for each value before execut
ing the statement. Values bound in this way are usu
ally treated as "SQL_VARCHAR" types unless the driver
can determine the correct type (which is rare), or
unless "bind_param" (or "bind_param_inout") has
already been used to specify the type.
"execute_array"
$rv = $sth->execute_array(attr) or die $sth->errstr;
$rv = $sth->execute_array(attr, @bind_values) or
die $sth->errstr;
Execute the prepared statement for each parameter
tuple provided either in the @bind_values, or by prior
calls to "bind_param_array".
An "undef" is returned if an error occurs. A success
ful "execute_array" always returns true regardless of
the number of rows affected, even if it's zero (see
below). It is always important to check the return
status of "execute_array" (and most other DBI methods)
for errors.
Parameters may be supplied either by prior calls to
"bind_param_array", or in the @bind_values argument.
The values supplied may be either scalars, or
arrayrefs. See "bind_param_array" for details.
The supplied "attr" hashref currently supports only
the "ArrayTupleStatus" attribute, which should specify
an arrayref to receive the status of each parameter
tuple bound to the statement. For parameter tuples
which are successfully executed, the element at the
same ordinal position in the status array will return
the resulting rowcount.
If a parameter tuple causes an error, the associated
status array element will be set to an arrayref of [
$sth->err, $sth->errstr ] returned by the failed exe
cution. If any tuple returns an error, "exe
cute_array" will return "undef" after it has executed
all the parameter tuples. In that case, the applica
tion should inspect the status array to determine
which parameter tuples failed.
If no "ArrayTupleStatus" is provided, "execute_array"
will return "undef" on the first occurance of a param
eter tuple causing an error. [XXX This may change as
it doesn't match the behaviour of drivers which use
bulk operation API to ship the data to the server.]
If all parameter tuples are successfully executed,
"execute_array" returns the sum of the number of rows
affected by all the parameter tuples, if known. If no
rows were affected, then "execute" returns "0E0",
which Perl will treat as 0 but will regard as true.
Note that it is not an error for no rows to be
affected by a statement. If the number of rows
affected is not known, then "execute_array" may return
a negative number. Applications should not rely on the
returned value to indicate actual total rowcounts, but
use the "ArrayTupleStatus" and explicitly inspect each
returned element of the status array.
Support for data returning statements is driver-spe
cific and subject to change. At present, the default
implementation provided by DBI only supports non-data
returning statements.
If any @bind_values are given, then "execute_array"
will effectively call "bind_param_array" for each
value before executing the statement. Values bound in
this way are usually treated as "SQL_VARCHAR" types
unless the driver can determine the correct type
(which is rare), or unless "bind_param",
"bind_param_inout", "bind_param_array", or
"bind_param_inout_array" has already been used to
specify the type.
Transaction semantics using array binding are driver
and database specific. If "AutoCommit" is on, the
default DBI implementation will cause each parameter
tuple to be inidividually committed (or rolled back in
the event of an error). If "AutoCommit" is off, the
application is responsible for explicitly committing
the entire set of bound parameter tuples. Note that
different drivers and databases may have different
behaviors when some parameter tuples cause failures.
In some cases, the driver or database may automati
cally rollback the effect of all prior parameter
tuples that succeeded in the transaction; other
drivers or databases may retain the effect of prior
successfully executed parameter tuples. Be sure to
check your driver and database for its specific behav
ior.
Note that, in general, performance will usually be
better with "AutoCommit" turned off, and using
explicit "commit" after each "execute_array" call.
"fetchrow_arrayref"
$ary_ref = $sth->fetchrow_arrayref;
$ary_ref = $sth->fetch; # alias
Fetches the next row of data and returns a reference
to an array holding the field values. Null fields are
returned as "undef" values in the array. This is the
fastest way to fetch data, particularly if used with
"$sth-">"bind_columns".
If there are no more rows or if an error occurs, then
"fetchrow_arrayref" returns an "undef". You should
check "$sth-">"err" afterwards (or use the "RaiseEr
ror" attribute) to discover if the "undef" returned
was due to an error.
Note that the same array reference is returned for
each fetch, so don't store the reference and then use
it after a later fetch. Also, the elements of the
array are also reused for each row, so take care if
you want to take a reference to an element. See also
"bind_columns".
"fetchrow_array"
@ary = $sth->fetchrow_array;
An alternative to "fetchrow_arrayref". Fetches the
next row of data and returns it as a list containing
the field values. Null fields are returned as "undef"
values in the list.
If there are no more rows or if an error occurs, then
"fetchrow_array" returns an empty list. You should
check "$sth-">"err" afterwards (or use the "RaiseEr
ror" attribute) to discover if the empty list returned
was due to an error.
If called in a scalar context for a statement handle
that has more than one column, it is undefined whether
the driver will return the value of the first column
or the last. So don't do that. Also, in a scalar con
text, an "undef" is returned if there are no more rows
or if an error occurred. That "undef" can't be distin
guished from an "undef" returned because the first
field value was NULL. For these reasons you should
exercise some caution if you use "fetchrow_array" in a
scalar context.
"fetchrow_hashref"
$hash_ref = $sth->fetchrow_hashref;
$hash_ref = $sth->fetchrow_hashref($name);
An alternative to "fetchrow_arrayref". Fetches the
next row of data and returns it as a reference to a
hash containing field name and field value pairs.
Null fields are returned as "undef" values in the
hash.
If there are no more rows or if an error occurs, then
"fetchrow_hashref" returns an "undef". You should
check "$sth-">"err" afterwards (or use the "RaiseEr
ror" attribute) to discover if the "undef" returned
was due to an error.
The optional $name parameter specifies the name of the
statement handle attribute. For historical reasons it
defaults to ""NAME"", however using either ""NAME_lc""
or ""NAME_uc"" is recomended for portability.
The keys of the hash are the same names returned by
"$sth-">"{$name}". If more than one field has the same
name, there will only be one entry in the returned
hash for those fields.
Because of the extra work "fetchrow_hashref" and Perl
have to perform, it is not as efficient as
"fetchrow_arrayref" or "fetchrow_array".
Currently, a new hash reference is returned for each
row. This will change in the future to return the same hash ref each time, so don't rely on the current
behaviour.
"fetchall_arrayref"
$tbl_ary_ref = $sth->fetchall_arrayref;
$tbl_ary_ref = $sth->fetchall_arrayref( $slice );
$tbl_ary_ref = $sth->fetchall_arrayref( $slice,
$max_rows );
The "fetchall_arrayref" method can be used to fetch
all the data to be returned from a prepared and exe
cuted statement handle. It returns a reference to an
array that contains one reference per row.
If there are no rows to return, "fetchall_arrayref"
returns a reference to an empty array. If an error
occurs, "fetchall_arrayref" returns the data fetched
thus far, which may be none. You should check
"$sth-">"err" afterwards (or use the "RaiseError"
attribute) to discover if the data is complete or was
truncated due to an error.
If $slice is an array reference, "fetchall_arrayref"
uses "fetchrow_arrayref" to fetch each row as an array
ref. If the parameter array is not empty then it is
used as a slice to select individual columns by perl
array index number (starting at 0, unlike column and
parameter numbers which start at 1).
With no parameters, or if $slice is undefined,
"fetchall_arrayref" acts as if passed an empty array
ref.
If $slice is a hash reference, "fetchall_arrayref"
uses "fetchrow_hashref" to fetch each row as a hash
reference. If the $slice hash is empty then
fetchrow_hashref() is simply called in a tight loop and the keys in the hashes have whatever name letter
case is returned by default from fetchrow_hashref.
(See "FetchHashKeyName" attribute.) If the $slice hash
is not empty, then it is used as a slice to select
individual columns by name. The values of the hash
should be set to 1. The key names of the returned
hashes match the letter case of the names in the
parameter hash, regardless of the "FetchHashKeyName"
attribute.
For example, to fetch just the first column of every
row:

$tbl_ary_ref = $sth->fetchall_arrayref([0]);
To fetch the second to last and last column of every
row:

$tbl_ary_ref = $sth->fetchall_arrayref([-2,-1]);
To fetch all fields of every row as a hash ref:

$tbl_ary_ref = $sth->fetchall_arrayref({});
To fetch only the fields called "foo" and "bar" of
every row as a hash ref (with keys named "foo" and
"BAR"):

$tbl_ary_ref = $sth->fetchall_arrayref({ foo=>1,
BAR=>1 });
The first two examples return a reference to an array
of array refs. The third and forth return a reference
to an array of hash refs.
If $max_rows is defined and greater than or equal to
zero then it is used to limit the number of rows
fetched before returning. fetchall_arrayref() can then be called again to fetch more rows. This is
especially useful when you need the better performance
of fetchall_arrayref() but don't have enough memory to fetch and return all the rows in one go.
"fetchall_hashref"
$hash_ref = $dbh->fetchall_hashref($key_field);
The "fetchall_hashref" method can be used to fetch all
the data to be returned from a prepared and executed
statement handle. It returns a reference to a hash
that contains, at most, one entry per row.
If there are no rows to return, "fetchall_hashref"
returns a reference to an empty hash. If an error
occurs, "fetchall_hashref" returns the data fetched
thus far, which may be none. You should check
"$sth-">"err" afterwards (or use the "RaiseError"
attribute) to discover if the data is complete or was
truncated due to an error.
The $key_field parameter provides the name of the
field that holds the value to be used for the key for
the returned hash. For example:

$dbh->{FetchHashKeyName} = 'NAME_lc';
$sth = $dbh->prepare("SELECT FOO, BAR, ID, NAME, BAZ
FROM TABLE");
$hash_ref = $sth->fetchall_hashref('id');
print "Name for id 42 is $hash_ref->{42}->{name}0;
The $key_field parameter can also be specified as an
integer column number (counting from 1). If
$key_field doesn't match any column in the statement,
as a name first then as a number, then an error is
returned.
This method is normally used only where the key field
value for each row is unique. If multiple rows are
returned with the same value for the key field then
later rows overwrite earlier ones.
"finish"
$rc = $sth->finish;
Indicates that no more data will be fetched from this
statement handle before it is either executed again or
destroyed. The "finish" method is rarely needed, but
can sometimes be helpful in very specific situations
to allow the server to free up resources (such as sort
buffers).
When all the data has been fetched from a "SELECT"
statement, the driver should automatically call "fin
ish" for you. So you should not normally need to call
it explicitly except when you know that you've not
fetched all the data from a statement handle. The
most common example is when you only want to fetch one
row, but in that case the "selectrow_*" methods may be
better anyway. Adding calls to "finish" after each
fetch loop is a common mistake, don't do it, it can
mask genuine problems like uncaught fetch errors.
Consider a query like:

SELECT foo FROM table WHERE bar=? ORDER BY foo
where you want to select just the first (smallest)
"foo" value from a very large table. When executed,
the database server will have to use temporary buffer
space to store the sorted rows. If, after executing
the handle and selecting one row, the handle won't be
re-executed for some time and won't be destroyed, the
"finish" method can be used to tell the server that
the buffer space can be freed.
Calling "finish" resets the "Active" attribute for the
statement. It may also make some statement handle
attributes (such as "NAME" and "TYPE") unavailable if
they have not already been accessed (and thus cached).
The "finish" method does not affect the transaction
status of the database connection. It has nothing to
do with transactions. It's mostly an internal "house
keeping" method that is rarely needed. See also "dis
connect" and the "Active" attribute.
The "finish" method should have been called "can
cel_select".
"rows"
$rv = $sth->rows;
Returns the number of rows affected by the last row
affecting command, or -1 if the number of rows is not
known or not available.
Generally, you can only rely on a row count after a
non-"SELECT" "execute" (for some specific operations
like "UPDATE" and "DELETE"), or after fetching all the
rows of a "SELECT" statement.
For "SELECT" statements, it is generally not possible
to know how many rows will be returned except by
fetching them all. Some drivers will return the num
ber of rows the application has fetched so far, but
others may return -1 until all rows have been fetched.
So use of the "rows" method or $DBI::rows with
"SELECT" statements is not recommended.
One alternative method to get a row count for a
"SELECT" is to execute a "SELECT COUNT(*) FROM ..."
SQL statement with the same "..." as your query and
then fetch the row count from that.
"bind_col"
$rc = $sth->bind_col($column_number, ar_to_bind);
Binds an output column (field) of a "SELECT" statement
to a Perl variable. See "bind_columns" below for an
example. Note that column numbers count up from 1.
Whenever a row is fetched from the database, the cor
responding Perl variable is automatically updated.
There is no need to fetch and assign the values manu
ally. The binding is performed at a very low level
using Perl aliasing so there is no extra copying tak
ing place. This makes using bound variables very
efficient.
For maximum portability between drivers, "bind_col"
should be called after "execute". This restriction may
be removed in a later version of the DBI.
You do not need to bind output columns in order to
fetch data, but it can be useful for some applications
which need either maximum performance or greater clar
ity of code. The "bind_param" method performs a simi
lar but opposite function for input variables.
"bind_columns"
$rc =
$sth->bind_columns(@list_of_refs_to_vars_to_bind);
Calls "bind_col" for each column of the "SELECT"
statement. The "bind_columns" method will die if the
number of references does not match the number of
fields.
For maximum portability between drivers,
"bind_columns" should be called after "execute".
For example:

$dbh->{RaiseError} = 1; # do this, or check every
call for errors
$sth = $dbh->prepare(q{ SELECT region, sales FROM
sales_by_region });
$sth->execute;
my ($region, $sales);
# Bind Perl variables to columns:
$rv = $sth->bind_columns(egion, ales);
# you can also use Perl's .) syntax (see perlref
docs):
# $sth->bind_columns(egion, $sales));
# Column binding is the most efficient way to fetch
data
while ($sth->fetch) {
print "$region: $sales0;
}
For compatibility with old scripts, the first parame
ter will be ignored if it is "undef" or a hash refer
ence.
Here's a more fancy example that binds columns to the
values inside a hash (thanks to H.Merijn Brand):

$sth->execute;
my %row;
$sth->bind_columns( @row{ @{$sth->{NAME_lc} } } ));
while ($sth->fetch) {
print "$row{region}: $row{sales}0;
}
"dump_results"
$rows = $sth->dump_results($maxlen, $lsep, $fsep,
$fh);
Fetches all the rows from $sth, calls "DBI::neat_list"
for each row, and prints the results to $fh (defaults
to "STDOUT") separated by $lsep (default "0). $fsep
defaults to ", " and $maxlen defaults to 35.
This method is designed as a handy utility for proto
typing and testing queries. Since it uses "neat_list"
to format and edit the string for reading by humans,
it is not recomended for data transfer applications.
Statement Handle Attributes
This section describes attributes specific to statement
handles. Most of these attributes are read-only.
Changes to these statement handle attributes do not affect
any other existing or future statement handles.
Attempting to set or get the value of an unknown attribute
is fatal, except for private driver specific attributes
(which all have names starting with a lowercase letter).
Example:

... = $h->{NUM_OF_FIELDS}; # get/read
Note that some drivers cannot provide valid values for
some or all of these attributes until after "$sth-">"exe
cute" has been called.
See also "finish" to learn more about the effect it may
have on some attributes.
"NUM_OF_FIELDS" (integer, read-only)
Number of fields (columns) the prepared statement will
return. Non-"SELECT" statements will have
"NUM_OF_FIELDS == 0".
"NUM_OF_PARAMS" (integer, read-only)
The number of parameters (placeholders) in the pre
pared statement. See SUBSTITUTION VARIABLES below for
more details.
"NAME" (array-ref, read-only)
Returns a reference to an array of field names for
each column. The names may contain spaces but should
not be truncated or have any trailing space. Note that
the names have the letter case (upper, lower or mixed)
as returned by the driver being used. Portable appli
cations should use "NAME_lc" or "NAME_uc".

print "First column name: $sth->{NAME}->[0]0;
"NAME_lc" (array-ref, read-only)
Like "NAME" but always returns lowercase names.
"NAME_uc" (array-ref, read-only)
Like "NAME" but always returns uppercase names.
"NAME_hash" (hash-ref, read-only)
"NAME_lc_hash" (hash-ref, read-only)
"NAME_uc_hash" (hash-ref, read-only)
The "NAME_hash", "NAME_lc_hash", and "NAME_uc_hash"
attributes return column name information as a refer
ence to a hash.
The keys of the hash are the names of the columns.
The letter case of the keys corresponds to the letter
case returned by the "NAME", "NAME_lc", and "NAME_uc"
attributes respectively (as described above).
The value of each hash entry is the perl index number
of the corresponding column (counting from 0). For
example:

$sth = $dbh->prepare("select Id, Name from table");
$sth->execute;
@row = $sth->fetchrow_array;
print "Name $row[ $sth->{NAME_lc_hash}{name} ]0;
"TYPE" (array-ref, read-only)
Returns a reference to an array of integer values for
each column. The value indicates the data type of the
corresponding column.
The values correspond to the international standards
(ANSI X3.135 and ISO/IEC 9075) which, in general
terms, means ODBC. Driver-specific types that don't
exactly match standard types should generally return
the same values as an ODBC driver supplied by the mak
ers of the database. That might include private type
numbers in ranges the vendor has officially registered
with the ISO working group:

ftp://sqlstandards.org/SC32/SQL_Registry/
Where there's no vendor-supplied ODBC driver to be
compatible with, the DBI driver can use type numbers
in the range that is now officially reserved for use
by the DBI: -9999 to -9000.
All possible values for "TYPE" should have at least
one entry in the output of the "type_info_all" method
(see "type_info_all").
"PRECISION" (array-ref, read-only)
Returns a reference to an array of integer values for
each column. For non-numeric columns, the value gen
erally refers to either the maximum length or the
defined length of the column. For numeric columns,
the value refers to the maximum number of significant
digits used by the data type (without considering a
sign character or decimal point). Note that for
floating point types (REAL, FLOAT, DOUBLE), the "dis
play size" can be up to 7 characters greater than the
precision. (for the sign + decimal point + the letter
E + a sign + 2 or 3 digits).
"SCALE" (array-ref, read-only)
Returns a reference to an array of integer values for
each column. NULL ("undef") values indicate columns
where scale is not applicable.
"NULLABLE" (array-ref, read-only)
Returns a reference to an array indicating the possi
bility of each column returning a null. Possible val
ues are 0 (or an empty string) = no, 1 = yes, 2 =
unknown.

print "First column may return NULL0 if $sth->{NUL
LABLE}->[0];
"CursorName" (string, read-only)
Returns the name of the cursor associated with the
statement handle, if available. If not available or if
the database driver does not support the "where cur
rent of ..." SQL syntax, then it returns "undef".
"ParamValues" (hash ref, read-only)
Returns a reference to a hash containing the values
currently bound to placeholders. Returns undef if not
supported by the driver. If the driver does support
"ParamValues" but no values have been bound yet then
either undef or an empty hash may be returned.
See "ShowErrorStatement" for an example of how this is
used.
It is possible that the values in the hash returned by
"ParamValues" are not exactly the same as those passed
to bind_param() or execute(). The driver may have modified the values in some way based on the TYPE the
value was bound with. For example a floating point
value bound as an SQL_INTEGER type may be returned as
an integer.
"Statement" (string, read-only)
Returns the statement string passed to the "prepare"
method.
"RowsInCache" (integer, read-only)
If the driver supports a local row cache for "SELECT"
statements, then this attribute holds the number of
un-fetched rows in the cache. If the driver doesn't,
then it returns "undef". Note that some drivers prefetch rows on execute, whereas others wait till the
first fetch.
See also the "RowCacheSize" database handle attribute.

FURTHER INFORMATION

Catalog Methods

An application can retrieve metadata information from the
DBMS by issuing appropriate queries on the views of the
Information Schema. Unfortunately, "INFORMATION_SCHEMA"
views are seldom supported by the DBMS. Special methods
(catalog methods) are available to return result sets for
a small but important portion of that metadata:
column_info
foreign_key_info
primary_key_info
table_info
All catalog methods accept arguments in order to restrict
the result sets. Passing "undef" to an optional argument
does not constrain the search for that argument. However,
an empty string ('') is treated as a regular search crite
ria and will only match an empty value.
Note: SQL/CLI and ODBC differ in the handling of empty
strings. An empty string will not restrict the result set
in SQL/CLI.
Most arguments in the catalog methods accept only ordinary values, e.g. the arguments of "primary_key_info()". Such arguments are treated as a literal string, i.e. the case
is significant and quote characters are taken literally.
Some arguments in the catalog methods accept search pat_ terns (strings containing '_' and/or '%'), e.g. the $table
argument of "column_info()". Passing '%' is equivalent to
leaving the argument "undef".
Caveat: The underscore ('_') is valid and often used in
SQL identifiers. Passing such a value to a search pattern
argument may return more rows than expected! To include
pattern characters as literals, they must be preceded by
an escape character which can be achieved with

$esc = $dbh->get_info( 14 ); # SQL_SEARCH_PATTERN_ES
CAPE
$search_pattern =~ s/([_%])/$esc$1/g;
The ODBC and SQL/CLI specifications define a way to change
the default behavior described above: All arguments
(except list value arguments) are treated as identifier if the "SQL_ATTR_METADATA_ID" attribute is set to "SQL_TRUE".
Quoted identifiers are very similar to ordinary values, i.e. their body (the string within the quotes) is inter
preted literally. Unquoted identifiers are compared in UPPERCASE.
The DBI (currently) does not support the "SQL_ATTR_META
DATA_ID" attribute, i.e. it behaves like an ODBC driver
where "SQL_ATTR_METADATA_ID" is set to "SQL_FALSE".
Transactions
Transactions are a fundamental part of any robust database
system. They protect against errors and database corrup
tion by ensuring that sets of related changes to the
database take place in atomic (indivisible, all-or-noth
ing) units.
This section applies to databases that support transac
tions and where "AutoCommit" is off. See "AutoCommit" for
details of using "AutoCommit" with various types of
databases.
The recommended way to implement robust transactions in
Perl applications is to use "RaiseError" and
"eval { ... }" (which is very fast, unlike "eval "..."").
For example:

$dbh->{AutoCommit} = 0; # enable transactions, if pos
sible
$dbh->{RaiseError} = 1;
eval {
foo(...) # do lots of work here
bar(...) # including inserts
baz(...) # and updates
$dbh->commit; # commit the changes if we get this
far
};
if ($@) {
warn "Transaction aborted because $@";
$dbh->rollback; # undo the incomplete changes
# add other application on-error-clean-up code here
}
If the "RaiseError" attribute is not set, then DBI calls
would need to be manually checked for errors, typically
like this:

$h->method(@args) or die $h->errstr;
With "RaiseError" set, the DBI will automatically "die" if
any DBI method call on that handle (or a child handle)
fails, so you don't have to test the return value of each
method call. See "RaiseError" for more details.
A major advantage of the "eval" approach is that the
transaction will be properly rolled back if any code (not
just DBI calls) in the inner application dies for any rea
son. The major advantage of using the "$h-">"{RaiseError}"
attribute is that all DBI calls will be checked automati
cally. Both techniques are strongly recommended.
After calling "commit" or "rollback" many drivers will not
let you fetch from a previously active "SELECT" statement
handle that's a child of the same database handle. A typi
cal way round this is to connect the the database twice
and use one connection for "SELECT" statements.
See "AutoCommit" and "disconnect" for other important
information about transactions.
Handling BLOB / LONG / Memo Fields
Many databases support "blob" (binary large objects),
"long", or similar datatypes for holding very long strings
or large amounts of binary data in a single field. Some
databases support variable length long values over
2,000,000,000 bytes in length.
Since values of that size can't usually be held in memory,
and because databases can't usually know in advance the
length of the longest long that will be returned from a
"SELECT" statement (unlike other data types), some special
handling is required.
In this situation, the value of the "$h-">"{LongReadLen}"
attribute is used to determine how much buffer space to
allocate when fetching such fields. The
"$h-">"{LongTruncOk}" attribute is used to determine how
to behave if a fetched value can't fit into the buffer.
When trying to insert long or binary values, placeholders
should be used since there are often limits on the maximum
size of an "INSERT" statement and the "quote" method gen
erally can't cope with binary data. See "Placeholders and
Bind Values".
Simple Examples
Here's a complete example program to select and fetch some
data:

my $dbh = DBI->connect("dbi:DriverName:db_name", $user,
$password)
or die "Can't connect to $data_source:
$DBI::errstr";
my $sth = $dbh->prepare( q{
SELECT name, phone
FROM mytelbook
}) or die "Can't prepare statement: $DBI::errstr";
my $rc = $sth->execute
or die "Can't execute statement: $DBI::errstr";
print "Query will return $sth->{NUM_OF_FIELDS} fields.0;
print "Field names: @{ $sth->{NAME} }0;
while (($name, $phone) = $sth->fetchrow_array) {
print "$name: $phone0;
}
# check for problems which may have terminated the fetch
early
die $sth->errstr if $sth->err;
$dbh->disconnect;
Here's a complete example program to insert some data from
a file. (This example uses "RaiseError" to avoid needing
to check each call).

my $dbh = DBI->connect("dbi:DriverName:db_name", $user,
$password, {
RaiseError => 1, AutoCommit => 0
});
my $sth = $dbh->prepare( q{
INSERT INTO table (name, phone) VALUES (?, ?)
});
open FH, "<phone.csv" or die "Unable to open phone.csv:
$!";
while (<FH>) {
chomp;
my ($name, $phone) = split /,/;
$sth->execute($name, $phone);
}
close FH;
$dbh->commit;
$dbh->disconnect;
Here's how to convert fetched NULLs (undefined values)
into empty strings:

while($row = $sth->fetchrow_arrayref) {
# this is a fast and simple way to deal with nulls:
foreach (@$row) { $_ = '' unless defined }
print "@$row0;
}
The "q{...}" style quoting used in these examples avoids
clashing with quotes that may be used in the SQL state
ment. Use the double-quote like "qq{...}" operator if you
want to interpolate variables into the string. See "Quote
and Quote-like Operators" in perlop for more details.
Threads and Thread Safety
Perl 5.7 and later support a new threading model called
iThreads. (The old and fatally flawed "5.005 style"
threads are not supported by the DBI.)
In the iThreads model each thread has it's own copy of the
perl interpreter. When a new thread is created the origi
nal perl interpreter is 'cloned' to create a new copy for
the new thread.
If the DBI and drivers are loaded and handles created
before the thread is created then it will get a cloned
copy of the DBI, the drivers and the handles.
However, the internal pointer data within the handles will
refer to the DBI and drivers in the original interpreter.
Using those handles in the new interpreter thread is not
safe, so the DBI detects this and croaks on any method
call using handles that don't belong to the current thread
(except for DESTROY).
Because of this (possibly temporary) restriction, newly
created threads must make their own connctions to the
database. Handles can't be shared across threads.
But BEWARE, some underlying database APIs (the code the
DBD driver uses to talk to the database, often supplied by
the database vendor) are not thread safe. If it's not
thread safe, then allowing more than one thread to enter
the code at the same time may cause subtle/serious prob
lems. In some cases allowing more than one thread to enter
the code, even if not at the same time, can cause prob
lems. You have been warned.
Using DBI with perl threads is not yet recommended for
production environments.
Signal Handling and Canceling Operations
The first thing to say is that signal handling in Perl is
currently not safe. There is always a small risk of Perl
crashing and/or core dumping when, or after, handling a
signal. (The risk was reduced with 5.004_04 but is still
present.)
The two most common uses of signals in relation to the DBI
are for canceling operations when the user types Ctrl-C
(interrupt), and for implementing a timeout using
"alarm()" and $SIG{ALRM}.
To assist in implementing these operations, the DBI pro
vides a "cancel" method for statement handles. The "can
cel" method should abort the current operation and is
designed to be called from a signal handler.
However, it must be stressed that: a) few drivers imple
ment this at the moment (the DBI provides a default method
that just returns "undef"); and b) even if implemented,
there is still a possibility that the statement handle,
and possibly the parent database handle, will not be
usable afterwards.
If "cancel" returns true, then it has successfully invoked
the database engine's own cancel function. If it returns
false, then "cancel" failed. If it returns "undef", then
the database engine does not have cancel implemented.
Subclassing the DBI
DBI can be subclassed and extended just like any other
object oriented module. Before we talk about how to do
that, it's important to be clear about how the DBI classes
and how they work together.
By default "$dbh = DBI-">"connect(...)" returns a $dbh
blessed into the "DBI::db" class. And the "$dbh-">"pre
pare" method returns an $sth blessed into the "DBI::st"
class (actually it simply changes the last four characters
of the calling handle class to be "::st").
The leading '"DBI"' is known as the 'root class' and the
extra '"::db"' or '"::st"' are the 'handle type suffixes'.
If you want to subclass the DBI you'll need to put your
overriding methods into the appropriate classes. For
example, if you want to use a root class of "MySubDBI" and
override the do(), prepare() and execute() methods, then your do() and prepare() methods should be in the "MySub DBI::db" class and the execute() method should be in the "MySubDBI::st" class.
To setup the inheritance hierarchy the @ISA variable in
"MySubDBI::db" should include "DBI::db" and the @ISA vari
able in "MySubDBI::st" should include "DBI::st". The
"MySubDBI" root class itself isn't currently used for any
thing visible and so, apart from setting @ISA to include
"DBI", it should be left empty.
So, having put your overriding methods into the right
classes, and setup the inheritance hierarchy, how do you
get the DBI to use them? You have two choices, either a
static method call using the name of your subclass:

$dbh = MySubDBI->connect(...);
or specifying a "RootClass" attribute:

$dbh = DBI->connect(..., { RootClass => 'MySubDBI' });
The only difference between the two is that using an
explicit RootClass attribute will make the DBI automati
cally attempt to load a module by that name (and not com
plain if such a module can't be found). If both forms are
used then the attribute takes precedence.
Here's a brief example of a DBI subclass. A more thorough
example can be found in t/subclass.t in the DBI distribu
tion.

package MySubDBI;
use strict;
use DBI;
use vars qw(@ISA);
@ISA = qw(DBI);
package MySubDBI::db;
use vars qw(@ISA);
@ISA = qw(DBI::db);
sub prepare {
my ($dbh, @args) = @_;
my $sth = $dbh->SUPER::prepare(@args)
or return;
$sth->{private_mysubdbi_info} = { foo => 'bar' };
return $sth;
}
package MySubDBI::st;
use vars qw(@ISA);
@ISA = qw(DBI::st);
sub fetch {
my ($sth, @args) = @_;
my $row = $sth->SUPER::fetch(@args)
or return;
do_something_magical_with_row_data($row)
or return $sth->set_err(1234, "The magic failed",
undef, "fetch");
return $row;
}
When calling a SUPER::method that returns a handle, be
careful to check the return value before trying to do
other things with it in your overridden method. This is
especially important if you want to set a hash attribute
on the handle, as Perl's autovivification will bite you by
(in)conveniently creating an unblessed hashref, which your
method will then return with usually baffling results
later on. It's best to check right after the call and
return undef immediately on error, just like DBI would and
just like the example above.
If your method needs to record an error it should call the
set_err() method with the error code and error string, as shown in the example above. The error code and error
string will be recorded in the handle and available via
"$h-">"err" and $DBI::errstr etc. The set_err() method always returns an undef or empty list as approriate. Since
your method should nearly always return an undef or empty
list as soon as an error is detected it's handy to simply
return what set_err() returns, as shown in the example above.
If the handle has "RaiseError", "PrintError", or "Han
dleError" etc. set then the set_err() method will honour them. This means that if "RaiseError" is set then
set_err() won't return in the normal way but will 'throw an exception' that can be caught with an "eval" block.
You can stash private data into DBI handles via
"$h-">"{private_..._*}". See the entry under "ATTRIBUTES
COMMON TO ALL HANDLES" for info and important caveats.

DEBUGGING

In addition to the "trace" method, you can enable the same
trace information by setting the "DBI_TRACE" environment
variable before starting Perl.

On Unix-like systems using a Bourne-like shell, you can do
this easily on the command line:
DBI_TRACE=2 perl your_test_script.pl
If "DBI_TRACE" is set to a non-numeric value, then it is
assumed to be a file name and the trace level will be set
to 2 with all trace output appended to that file. If the
name begins with a number followed by an equal sign ("="),
then the number and the equal sign are stripped off from
the name, and the number is used to set the trace level.
For example: a

Pure-Perl DBI

A pure-perl emulation of the DBI is included in the dis
tribution for people using pure-perl drivers who, for
whatever reason, can't install the compiled DBI. See
DBI::PurePerl.

SEE ALSO

Driver and Database Documentation

Refer to the documentation for the DBD driver that you are
using.

Refer to the SQL Language Reference Manual for the
database engine that you are using.

Standards Reference Information

More detailed information about the semantics of certain
DBI methods that are based on ODBC and SQL/CLI standards
is available on-line via microsoft.com, for ODBC, and
www.jtc1sc32.org for the SQL/CLI standard:
DBI method ODBC function SQL/CLI Working Draft
---------- ------------- --------------------column_info SQLColumns Page 124
foreign_key_info SQLForeignKeys Page 163
get_info SQLGetInfo Page 214
primary_key_info SQLPrimaryKeys Page 254
table_info SQLTables Page 294
type_info SQLGetTypeInfo Page 239
For example, for ODBC information on SQLColumns you'd
visit:

http://msdn.microsoft.com/library/en-us/odbc/htm/odbc
sqlcolumns.asp
If that URL ceases to work then use the MSDN search facil
ity at:

http://search.microsoft.com/us/dev/
and search for "SQLColumns returns" using the exact phrase
option. The link you want will probably just be called
"SQLColumns" and will be part of the Data Access SDK.
And for SQL/CLI standard information on SQLColumns you'd
read page 124 of the (very large) SQL/CLI Working Draft
available from:

http://www.jtc1sc32.org/sc32/jtc1sc32.nsf/Attach
ments/7E3B41486BD99C3488256B410064C877/$FILE/32N0744T.PDF
A hyperlinked, browsable version of the BNF syntax for
SQL92 (plus Oracle 7 SQL and PL/SQL) is available here:

http://cui.unige.ch/db-research/Enseignement/analysein
fo/SQL92/BNFindex.html
A BNF syntax for SQL3 is available here:

http://www.sqlstandards.org/SC32/WG3/Progression_Docu
ments/Informal_working_drafts/iso-9075-2-1999.bnf
Books and Journals

Programming the Perl DBI, by Alligator Descartes and Tim
Bunce.
Programming Perl 2nd Ed. by Larry Wall, Tom Christiansen
& Randal Schwartz.
Learning Perl by Randal Schwartz.
Dr Dobb's Journal, November 1996.
The Perl Journal, April 1997.
Perl Modules
Index of DBI related modules available from CPAN:

http://search.cpan.org/search?mode=mod
ule&query=DBIx%3A%3A
http://search.cpan.org/search?mode=doc&query=DBI
For a good comparison of RDBMS-OO mappers and some OORDBMS mappers (including Class::DBI, Alzabo, and
DBIx::RecordSet in the former category and Tangram and
SPOPS in the latter) see the Perl Object-Oriented Persis
tence project pages at:

http://poop.sourceforge.net
Manual Pages
perl(1), perlmod(1), perlbook(1)
Mailing List
The dbi-users mailing list is the primary means of commu nication among users of the DBI and its related modules.
For details send email to:

dbi-users-help@perl.org
There are typically between 700 and 900 messages per
month. You have to subscribe in order to be able to post.
However you can opt for a 'post-only' subscription.
Mailing list archives (of variable quality) are held at:

http://www.xray.mpe.mpg.de/mailing-lists/dbi/
http://groups.yahoo.com/group/dbi-users
http://www.bitmechanic.com/mail-archives/dbi-users/
http://marc.theaimsgroup.com/?l=perl-dbi&r=1&w=2
http://www.mail-archive.com/dbi-users%40perl.org/
Assorted Related WWW Links
The DBI "Home Page":

http://dbi.perl.org/
Other DBI related links:

http://tegan.deltanet.com/~phlip/DBUIdoc.html
http://dc.pm.org/perl_db.html
http://wdvl.com/Authoring/DB/Intro/toc.html
http://www.hotwired.com/webmonkey/backend/tutorials/tuto
rial1.html
http://bumppo.net/lists/macperl/1999/06/msg00197.html
Other database related links:

http://www.jcc.com/sql_stnd.html
http://cuiwww.unige.ch/OSG/info/FreeDB/FreeDB.home.html
Commercial and Data Warehouse Links

http://www.dwinfocenter.org
http://www.datawarehouse.com
http://www.datamining.org
http://www.olapcouncil.org
http://www.idwa.org
http://www.knowledgecenters.org/dwcenter.asp
Recommended Perl Programming Links

http://language.perl.com/style/
FAQ
Please also read the DBI FAQ which is installed as a
DBI::FAQ module. You can use perldoc to read it by exe
cuting the "perldoc DBI::FAQ" command.

AUTHORS

DBI by Tim Bunce. This pod text by Tim Bunce, J. Douglas
Dunlop, Jonathan Leffler and others. Perl by Larry Wall
and the "perl5-porters".

COPYRIGHT

The DBI module is Copyright (c) 1994-2002 Tim Bunce. Ire
land. All rights reserved.

You may distribute under the terms of either the GNU Gen
eral Public License or the Artistic License, as specified
in the Perl README file.

ACKNOWLEDGEMENTS

I would like to acknowledge the valuable contributions of
the many people I have worked with on the DBI project,
especially in the early years (1992-1994). In no particu
lar order: Kevin Stock, Buzz Moschetti, Kurt Andersen, Ted
Lemon, William Hails, Garth Kennedy, Michael Peppler, Neil
S. Briscoe, Jeff Urlwin, David J. Hughes, Jeff Stander,
Forrest D Whitcher, Larry Wall, Jeff Fried, Roy Johnson,
Paul Hudson, Georg Rehfeld, Steve Sizemore, Ron Pool, Jon
Meek, Tom Christiansen, Steve Baumgarten, Randal Schwartz,
and a whole lot more.

Then, of course, there are the poor souls who have strug
gled through untold and undocumented obstacles to actually
implement DBI drivers. Among their ranks are Jochen Wied
mann, Alligator Descartes, Jonathan Leffler, Jeff Urlwin,
Michael Peppler, Henrik Tougaard, Edwin Pratomo, Davide
Migliavacca, Jan Pazdziora, Peter Haworth, Edmund Mergl,
Steve Williams, Thomas Lowery, and Phlip Plumlee. Without
them, the DBI would not be the practical reality it is
today. I'm also especially grateful to Alligator
Descartes for starting work on the "Programming the Perl
DBI" book and letting me jump on board.

Much of the DBI and DBD::Oracle was developed while I was
Technical Director (CTO) of the Paul Ingram Group
(www.ig.co.uk). So I'd especially like to thank Paul for
his generosity and vision in supporting this work for many
years.

TRANSLATIONS

A German translation of this manual (possibly slightly out
of date) is available, thanks to O'Reilly, at:
http://www.oreilly.de/catalog/perldbiger/
Some other translations:

http://cronopio.net/perl/
Spanish
http://member.nifty.ne.jp/hippo2000/dbimemo.htm
Japanese

SUPPORT / WARRANTY

The DBI is free software. IT COMES WITHOUT WARRANTY OF ANY
KIND.

Commercial support for Perl and the DBI, DBD::Oracle and
Oraperl modules can be arranged via The Perl Clinic. For
more details visit:
http://www.perlclinic.com
For direct DBI and DBD::Oracle support, enhancement, and
related work I am available for consultancy on standard
commercial terms.

TRAINING

References to DBI related training resources. No recommen
dation implied.
http://www.treepax.co.uk/
http://www.keller.com/dbweb/

FREQUENTLY ASKED QUESTIONS

See the DBI FAQ for a more comprehensive list of FAQs. Use
the "perldoc DBI::FAQ" command to read it.

How fast is the DBI?

To measure the speed of the DBI and DBD::Oracle code, I
modified DBD::Oracle so you can set an attribute that will
cause the same row to be fetched from the row cache over
and over again (without involving Oracle code but exercis
ing *all* the DBI and DBD::Oracle code in the code path
for a fetch).

The results (on my lightly loaded old Sparc 10) fetching
50000 rows using:
1 while $csr->fetch;
were: one field: 5300 fetches per cpu second
(approx) ten fields: 4000 fetches per cpu second
(approx)
Obviously results will vary between platforms (newer
faster platforms can reach around 50000 fetches per sec
ond), but it does give a feel for the maximum performance:
fast. By way of comparison, using the code:

1 while @row = $csr->fetchrow_array;
("fetchrow_array" is roughly the same as "ora_fetch")
gives:

one field: 3100 fetches per cpu second (approx)
ten fields: 1000 fetches per cpu second (approx)
Notice the slowdown and the more dramatic impact of extra
fields. (The fields were all one char long. The impact
would be even bigger for longer strings.)
Changing that slightly to represent actually doing some
thing in Perl with the fetched data:

while(@row = $csr->fetchrow_array) {
$hash{++$i} = [ @row ];
}
gives: ten fields: 500 fetches per cpu second (approx)
That simple addition has *halved* the performance.
I therefore conclude that DBI and DBD::Oracle overheads
are small compared with Perl language overheads (and prob
ably database overheads).
So, if you think the DBI or your driver is slow, try
replacing your fetch loop with just:

1 while $csr->fetch;
and time that. If that helps then point the finger at your
own code. If that doesn't help much then point the finger
at the database, the platform, the network etc. But think
carefully before pointing it at the DBI or your driver.
(Having said all that, if anyone can show me how to make
the DBI or drivers even more efficient, I'm all ears.)
Why doesn't my CGI script work right?
Read the information in the references below. Please do
not post CGI related questions to the dbi-users mailing list (or to me).

http://www.perl.com/cgi-bin/pace/pub/doc/FAQs/cgi/perl
cgi-faq.html
http://www3.pair.com/webthing/docs/cgi/faqs/cgifaq.shtml
http://www-genome.wi.mit.edu/WWW/faqs/www-security
faq.html
http://www.boutell.com/faq/
http://www.perl.com/perl/faq/
General problems and good ideas:

Use the CGI::ErrorWrap module.
Remember that many env vars won't be set for CGI scripts.
How can I maintain a WWW connection to a database?
For information on the Apache httpd server and the
"mod_perl" module see

http://perl.apache.org/
What about ODBC?
A DBD::ODBC module is available.
Does the DBI have a year 2000 problem?
No. The DBI has no knowledge or understanding of dates at
all.
Individual drivers (DBD::*) may have some date handling
code but are unlikely to have year 2000 related problems
within their code. However, your application code which
uses the DBI and DBD drivers may have year 2000 related
problems if it has not been designed and written well.
See also the "Does Perl have a year 2000 problem?" section
of the Perl FAQ:

http://www.perl.com/CPAN/doc/FAQs/FAQ/PerlFAQ.html

OTHER RELATED WORK AND PERL MODULES

Apache::DBI by E.Mergl@bawue.de
To be used with the Apache daemon together with an
embedded Perl interpreter like "mod_perl". Establishes
a database connection which remains open for the life
time of the HTTP daemon. This way the CGI connect and
disconnect for every database access becomes superflu
ous.
JDBC Server by Stuart 'Zen' Bishop zen@bf.rmit.edu.au
The server is written in Perl. The client classes that
talk to it are of course in Java. Thus, a Java applet
or application will be able to comunicate via the JDBC
API with any database that has a DBI driver installed.
The URL used is in the form
"jdbc:dbi://host.domain.etc:999/Driver/DBName". It
seems to be very similar to some commercial products,
such as jdbcKona.
Remote Proxy DBD support
As of DBI 1.02, a complete implementation of a
DBD::Proxy driver and the DBI::ProxyServer are part of
the DBI distribution.
SQL Parser
See also the SQL::Statement module, a very simple SQL
parser and engine, base of the DBD::CSV driver.

perl v5.8.0 2002-07-18 DBI(3)

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