DBD::SQLite(3p)

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 <http://www.sqlite.org/>.

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 <http://www.sqlite.org/lang.html> 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 (this feature is currently disabled for perl < 5.8.5). 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 bizarreness in SQLite's type system (see <http://www.sqlite.org/datatype3.html>), 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.

Generally you should not be using this method. Use the DBI last_insert_id method instead. The usage of this is:

  $h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])

Running "$h->last_insert_id("","","","")" is the equivalent of running "$dbh->func('last_insert_rowid')" directly.

  $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. The driver will check that this is a proper sorting function.

Collations "binary" and "nocase" are builtin within SQLite. Collations "perl" and "perllocale" are builtin within the DBD::SQLite driver, and correspond to the Perl "cmp" operator with or without the locale pragma; so you can write for example

  CREATE TABLE foo(
      txt1 COLLATE perl,
      txt2 COLLATE perllocale,
      txt3 COLLATE nocase
  )

or

  SELECT * FROM foo ORDER BY name COLLATE perllocale

If the attribute "$dbh->{unicode}" is set, strings coming from the database and passed to the collation function will be properly tagged with the utf8 flag; but this only works if the "unicode" attribute is set before the call to "create_collation". The recommended way to activate unicode is to set the parameter at connection time :

  my $dbh = DBI->connect(
      "dbi:SQLite:dbname=foo", "", "",
      {
          RaiseError => 1,
          unicode    => 1,
      }
  );

  $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;

For more examples, see the DBD::SQLite::Cookbook.

  $dbh->func( $n_opcodes, $code_ref, 'progress_handler' )
This method registers a handler to be invoked periodically during long running calls to SQLite.

An example use for this interface is to keep a GUI updated during a large query. The parameters are:

$n_opcodes
    The progress handler is invoked once for every $n_opcodes virtual machine opcodes in SQLite.

$handler
    Reference to the handler subroutine. If the progress handler returns non-zero, the SQLite operation is interrupted. This feature can be used to implement a "Cancel" button on a GUI dialog box.

    Set this argument to "undef" if you want to unregister a previous progress handler.

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 (<http://axkit.org>), 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.

The memory usage of SQLite can also be tuned using the cache_size pragma.

  $dbh->do("PRAGMA cache_size = 800000");

The above will allocate 800M for DB cache; the default is 2M. Your sweet spot probably lies somewhere in between.

TO DO
The following items remain to be done.

  Warnings Upgrade
We currently use a horridly hacky method to issue and suppress warnings. It suffices for now, but just barely.

Migrate all of the warning code to use the recommended DBI warnings.

  Leak Detection
Implement one or more leak detection tests that only run during AUTOMATED_TESTING and RELEASE_TESTING and validate that none of the C code we work with leaks.

SUPPORT
Bugs should be reported via the CPAN bug tracker at

<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>

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.

<http://rt.cpan.org/Public/Bug/Display.html?id=35449> (breaks tests)

<http://rt.cpan.org/Public/Bug/Display.html?id=29629> (requires a patch)

<http://rt.cpan.org/Public/Bug/Display.html?id=29058> (requires a patch)

Switch tests to Test::More to support more advanced testing behaviours

AUTHOR
Matt Sergeant <matt@sergeant.org>

Francis J. Lacoste <flacoste@logreport.org>

Wolfgang Sourdeau <wolfgang@logreport.org>

Adam Kennedy <adamk@cpan.org>

Max Maischein <corion@cpan.org>

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.

Some parts copyright 2008 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.