NAME

       DBD::SQLite2 - Self Contained RDBMS in a DBI Driver (sqlite 2.x)

SYNOPSIS

         use DBI;
         my $dbh = DBI->connect("dbi:SQLite2: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::SQLite2
       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.

       For real work please use the updated DBD::SQLite driver with the up-to-date sqlite3
       backend.  SQLite2 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::SQLite2 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 SQLite2 database.

DRIVER PRIVATE ATTRIBUTES

   Database Handle Attributes
       sqlite_version
           Returns the version of the SQLite library which DBD::SQLite2 is using, i.e, "2.8.15".

       sqlite_encoding
           Returns either "UTF-8" or "iso8859" to indicate how the SQLite library was compiled.

       sqlite_handle_binary_nulls
           Set this attribute to 1 to transparently handle binary nulls in quoted and returned
           data.

           NOTE: This will cause all backslash characters ("\") to be doubled up in all columns
           regardless of whether or not they contain binary data or not. This may break your
           database if you use it from another application. This does not use the built in
           "sqlite_encode_binary" and "sqlite_decode_binary" functions, which may be considered a
           bug.

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.

   $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:

       $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.

       $func_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, $argc, $pkg, 'create_aggregate' )
       This method will register a new aggregate function which can then 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 rows 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;

NOTES

       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::SQLite2 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.

BUGS

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

AUTHOR

       Matt Sergeant, matt@sergeant.org

       Perl extension functions contributed by Francis J. Lacoste <flacoste@logreport.org> and
       Wolfgang Sourdeau <wolfgang@logreport.org>.  Maintenance help by Reini Urban
       <rurban@cpan.org>

SEE ALSO

       DBD::SQLite, DBI.