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MAN page from Mandriva 2010 perl-DBD-SQLite2-0.330.0-1mdv2010.0.i586.rpm

DBD::SQLite2

Section: User Contributed Perl Documentation (3)
Updated: 2004-09-10
Index 

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 findat http://www.hwaci.com/sw/sqlite/.

Rather than ask you to install SQLite first, because SQLite is publicdomain, DBD::SQLite2 includes the entire thing in the distribution. Soin order to get a fast transaction capable RDBMS working for yourperl project you simply have to install this module, and nothingelse.

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, making iteasier 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 theSQL parser.

There's lots more to it, so please refer to the docs on the SQLite webpage, listed above, for SQL details. Also refer to DBI for detailson how to use DBI itself. 

CONFORMANCE WITH DBI SPECIFICATION

The API works like every DBI module does. Please see DBI for moredetails about core features.

Currently many statement attributes are not implemented or arelimited 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::SQLite2 is using, e.g., ``2.8.0''.
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 quotedand returned data.

NOTE: This will cause all backslash characters ("\") to be doubledup in all columns regardless of whether or not they contain binarydata or not. This may break your database if you use it from anotherapplication. This does not use the built in sqlite_encode_binaryand 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 PRIMARYKEY 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 SQLquery. The method's parameters are:
$name
The name of the function. This is the name of the function as it willbe 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 thecurrent 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 usedfrom SQL. The method's parameters are:
$name
The name of the aggregate function, this is the name under which thefunction will be available from SQL.
$argc
This is an integer which tells the SQL parser how many arguments thefunction takes. If that number is -1, the function can take any numberof 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 shouldbe used to aggregate the rows in a particular group. The step() andfinalize() methods will be called upon the reference return bythe 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 wereprocessed and it should return the aggregate function's result. Whenthere is no rows in the aggregate, finalize() will be called rightafter 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 withthe 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 conflictingwith 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 committingevery 1000 rows (otherwise the insertion is quite slow), and then performingqueries 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 itreturned within 2 seconds. I'm seriously considering switching my loganalysis 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 areusing linux. Also you might want to set:

  PRAGMA default_synchronous = OFF

Which will prevent sqlite from doing fsync's when writing (whichslows down non-transactional writes significantly) at the expense of somepeace 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, mattAATTsergeant.org

Perl extension functions contributed by Francis J. Lacoste<flacosteAATTlogreport.org> and Wolfgang Sourdeau<wolfgangAATTlogreport.org> 

SEE ALSO

DBI.


 

Index

NAME
SYNOPSIS
DESCRIPTION
CONFORMANCE WITH DBI SPECIFICATION
DRIVER PRIVATE ATTRIBUTES
Database Handle Attributes
DRIVER PRIVATE METHODS
$dbh->func('last_insert_rowid')
$dbh->func( $name, $argc, $func_ref, create_function )
$dbh->func( $name, $argc, $pkg, 'create_aggregate' )
NOTES
PERFORMANCE
BUGS
AUTHOR
SEE ALSO

This document was created byman2html,using the manual pages.