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DBD::SQLite(3)	      User Contributed Perl Documentation	DBD::SQLite(3)

       DBD::SQLite - Self Contained RDBMS in a DBI Driver

	 use DBI;
	 my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile","","");

       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 http://www.hwaci.com/sw/sqlite/lang.html for details.

       A complete DB in a single disk file
	   Everything for your database is stored in a single disk file, mak‐
	   ing 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 transac‐

	   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.

       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.

       Database Handle Attributes

	   Returns the version of the SQLite library which DBD::SQLite is
	   using, e.g., "2.8.0". Can only be read.

	   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
	   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 explicitely
	   using the 3-argument form of "bind_param" in DBI when doing

	       use DBI qw(:sql_types);
	       $dbh->{unicode} = 1;
	       my $sth = $dbh->prepare
		    ("INSERT INTO mytable (blobcolumn) VALUES (?)");
	       $sth->bind_param(1, $binary_data, SQL_BLOB); # binary_data will
	       # be stored as-is.

	   Defining the column type as BLOB in the DDL is not sufficient.


       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 ver‐
       sion 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, $func_ref, "create_function" )

       This method will register a new function which will be useable in SQL
       query. The method's parameters are:

	   The name of the function. This is the name of the function as it
	   will be used from SQL.

	   The number of arguments taken by the function. If this number is
	   -1, the function can take any number of arguments.

	   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, $argc, $pkg, 'create_aggregate' )

       This method will register a new aggregate function which can then used
       from SQL. The method's parameters are:

	   The name of the aggregate function, this is the name under which
	   the function will be available from SQL.

	   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.

	   This is the package which implements the aggregator interface.

       The aggregator interface consists of defining three methods:

	   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

	   This method will be called once for each rows in the aggregate.

	   This method will be called once all rows in the aggregate were pro‐
	   cessed 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;

       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:/path/to/db");

	 my $blob = `cat foo.jpg`;
	 my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
	 $sth->bind_param(1, $blob, SQL_BLOB);

       And then retreival just works:

	 $sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
	 my $row = $sth->fetch;
	 my $blobo = $row->[1];

	 # now $blobo == $blob

       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 con‐
       flicting with DBD::SQLite and use the supplied "sqlite" command line

       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.

       Likely to be many, please use http://rt.cpan.org/ for reporting bugs.

       Matt Sergeant, matt@sergeant.org

       Perl extension functions contributed by Francis J. Lacoste <fla‐
       coste@logreport.org> and Wolfgang Sourdeau <wolfgang@logreport.org>


perl v5.8.8			  2007-08-23			DBD::SQLite(3)

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