NAME
DBD::SQLite - Self Contained RDBMS in a DBI Driver
SYNOPSIS
use DBI;
my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile","","");
DESCRIPTION
SQLite is a public domain RDBMS database engine that you can find at
.
Rather than ask you to install SQLite first, because SQLite is public
domain, DBD::SQLite includes the entire thing in the distribution. So in
order to get a fast transaction capable RDBMS working for your perl
project you simply have to install this module, and nothing else.
SQLite supports the following features:
Implements a large subset of SQL92
See for details.
A complete DB in a single disk file
Everything for your database is stored in a single disk file, making
it easier to move things around than with DBD::CSV.
Atomic commit and rollback
Yes, DBD::SQLite is small and light, but it supports full
transactions!
Extensible
User-defined aggregate or regular functions can be registered with
the SQL parser.
There's lots more to it, so please refer to the docs on the SQLite web
page, listed above, for SQL details. Also refer to DBI for details on
how to use DBI itself.
CONFORMANCE WITH DBI SPECIFICATION
The API works like every DBI module does. Please see DBI for more
details about core features.
Currently many statement attributes are not implemented or are limited
by the typeless nature of the SQLite database.
DRIVER PRIVATE ATTRIBUTES
Database Handle Attributes
sqlite_version
Returns the version of the SQLite library which DBD::SQLite is
using, e.g., "2.8.0". Can only be read.
unicode
If set to a true value, DBD::SQLite will turn the UTF-8 flag on for
all text strings coming out of the database. For more details on the
UTF-8 flag see perlunicode. The default is for the UTF-8 flag to be
turned off.
Also note that due to some bizareness in SQLite's type system (see
), if you want to retain
blob-style behavior for some columns under "$dbh->{unicode} = 1"
(say, to store images in the database), you have to state so
explicitly using the 3-argument form of "bind_param" in DBI when
doing updates:
use DBI qw(:sql_types);
$dbh->{unicode} = 1;
my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");
# Binary_data will be stored as is.
$sth->bind_param(1, $binary_data, SQL_BLOB);
Defining the column type as "BLOB" in the DDL is not sufficient.
DRIVER PRIVATE METHODS
$dbh->func('last_insert_rowid')
This method returns the last inserted rowid. If you specify an INTEGER
PRIMARY KEY as the first column in your table, that is the column that
is returned. Otherwise, it is the hidden ROWID column. See the sqlite
docs for details.
Note: You can now use $dbh->last_insert_id() if you have a recent
version of DBI.
$dbh->func('busy_timeout')
Retrieve the current busy timeout.
$dbh->func( $ms, 'busy_timeout' )
Set the current busy timeout. The timeout is in milliseconds.
$dbh->func( $name, $argc, $code_ref, "create_function" )
This method will register a new function which will be useable in an SQL
query. The method's parameters are:
$name
The name of the function. This is the name of the function as it
will be used from SQL.
$argc
The number of arguments taken by the function. If this number is -1,
the function can take any number of arguments.
$code_ref
This should be a reference to the function's implementation.
For example, here is how to define a now() function which returns the
current number of seconds since the epoch:
$dbh->func( 'now', 0, sub { return time }, 'create_function' );
After this, it could be use from SQL as:
INSERT INTO mytable ( now() );
$dbh->func( $name, $code_ref, "create_collation" )
This method will register a new function which will be useable in an SQL
query as a COLLATE option for sorting. The method's parameters are:
$name
The name of the function. This is the name of the function as it
will be used from SQL.
$code_ref
This should be a reference to the function's implementation.
By default, the collations "perl" and "perllocale" are created for you.
These allow sorting in Perl terms using "cmp", in both locale and
non-locale forms. For example, the following does a locale-aware Perl
cmp sort.
SELECT * FROM foo ORDER BY name COLLATE perllocale
$dbh->func( $name, $argc, $pkg, 'create_aggregate' )
This method will register a new aggregate function which can then be
used from SQL. The method's parameters are:
$name
The name of the aggregate function, this is the name under which the
function will be available from SQL.
$argc
This is an integer which tells the SQL parser how many arguments the
function takes. If that number is -1, the function can take any
number of arguments.
$pkg
This is the package which implements the aggregator interface.
The aggregator interface consists of defining three methods:
new()
This method will be called once to create an object which should be
used to aggregate the rows in a particular group. The step() and
finalize() methods will be called upon the reference return by the
method.
step(@_)
This method will be called once for each row in the aggregate.
finalize()
This method will be called once all rows in the aggregate were
processed and it should return the aggregate function's result. When
there is no rows in the aggregate, finalize() will be called right
after new().
Here is a simple aggregate function which returns the variance (example
adapted from pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($x - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->func( "variance", 1, 'variance', "create_aggregate" );
The aggregate function can then be used as:
SELECT group_name, variance(score)
FROM results
GROUP BY group_name;
BLOBS
As of version 1.11, blobs should "just work" in SQLite as text columns.
However this will cause the data to be treated as a string, so SQL
statements such as length(x) will return the length of the column as a
NUL terminated string, rather than the size of the blob in bytes. In
order to store natively as a BLOB use the following code:
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:dbfile","","");
my $blob = `cat foo.jpg`;
my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
$sth->bind_param(1, $blob, SQL_BLOB);
$sth->execute();
And then retrieval just works:
$sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
$sth->execute();
my $row = $sth->fetch;
my $blobo = $row->[1];
# now $blobo == $blob
NOTES
Although the database is stored in a single file, the directory
containing the database file must be writable by SQLite because the
library will create several temporary files there.
To access the database from the command line, try using dbish which
comes with the DBI module. Just type:
dbish dbi:SQLite:foo.db
On the command line to access the file foo.db.
Alternatively you can install SQLite from the link above without
conflicting with DBD::SQLite and use the supplied "sqlite" command line
tool.
PERFORMANCE
SQLite is fast, very fast. I recently processed my 72MB log file with
it, inserting the data (400,000+ rows) by using transactions and only
committing every 1000 rows (otherwise the insertion is quite slow), and
then performing queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to
return, but what surprised me most of all was:
SELECT url, count(*) as count
FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20
To discover the top 20 hit URLs on the site (), and it
returned within 2 seconds. I'm seriously considering switching my log
analysis code to use this little speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
For best performance be sure to tune your hdparm settings if you are
using linux. Also you might want to set:
PRAGMA default_synchronous = OFF
Which will prevent sqlite from doing fsync's when writing (which slows
down non-transactional writes significantly) at the expense of some
peace of mind. Also try playing with the cache_size pragma.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
TO DO
There're several pended RT bugs/patches at the moment (mainly due to the
lack of tests/patches or segfaults on tests).
Here's the list.
(patch required)
(patch required,
and the following tests may break)
(need to see what
is the best solution right now)
(patch required)
(test required)
(break tests)
(patch required)
Switch tests to Test::More to support more advanced testing behaviours
AUTHOR
Matt Sergeant
Francis J. Lacoste
Wolfgang Sourdeau
Adam Kennedy
Max Maischein
COPYRIGHT
The bundled SQLite code in this distribution is Public Domain.
DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.
Some parts copyright 2008 Francis J. Lacoste and Wolfgang Sourdeau.
Some parts copyright 2008 - 2009 Adam Kennedy.
Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey
Tang.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
The full text of the license can be found in the LICENSE file included
with this module.