dbd::sqlite::cookbook(3) [suse man page]

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

NAME

       DBD::SQLite::Cookbook - The DBD::SQLite Cookbook

DESCRIPTION

       This is the DBD::SQLite cookbook.

       It is intended to provide a place to keep a variety of functions and formals for use in callback APIs in DBD::SQLite.

   Variance
       This is a simple aggregate function which returns a variance. It is adapted from an example implementation in 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;
	 }

	 # NOTE: If you use an older DBI (< 1.608),
	 # use $dbh->func(..., "create_aggregate") instead.
	 $dbh->sqlite_create_aggregate( "variance", 1, 'variance' );

       The function can then be used as:

	 SELECT group_name, variance(score)
	 FROM results
	 GROUP BY group_name;

   Variance (Memory Efficient)
       A more efficient variance function, optimized for memory usage at the expense of precision:

	 package variance2;

	 my $sum   = 0;
	 my $count = 0;
	 my %hash;

	 sub new { bless [], shift; }

	 sub step {
	     my ( $self, $value ) = @_;

	     # by truncating and hashing, we can comsume many more data points
	     $value = int($value); # change depending on need for precision
				   # use sprintf for arbitrary fp precision
	     if (defined $hash{$value}) {
		 $hash{$value}++;
	     } else {
		 $hash{$value} = 1;
	     }
	     $sum += $value;
	     $count++;
	 }

	 sub finalize {
	     my $self = $_[0];

	     # Variance is NULL unless there is more than one row
	     return undef unless $count > 1;

	     # calculate avg
	     my $mu = $sum / $count;

	     my $sigma = 0;
	     foreach my $h (keys %hash) {
		 $sigma += (($h - $mu)**2) * $hash{$h};
	     }
	     $sigma = $sigma / ($count - 1);

	     return $sigma;
	 }

       The function can then be used as:

	 SELECT group_name, variance2(score)
	 FROM results
	 GROUP BY group_name;

   Variance (Highly Scalable)
       A third variable implementation, designed for arbitrarily large data sets:

	 package variance;

	 my $mu = 0;
	 my $count = 0;
	 my $S = 0

	 sub new { bless [], shift; }

	 sub step {
	     my ( $self, $value ) = @_;
	     $count++;
	     $delta = $value - $mu;
	     $mu = $mu + $delta/$count
	     $S = $S + $delta*($value - $mu);
	 }

	 sub finalize {
	     my $self = $_[0];
	     return $S / ($count - 1);
	 }

       The function can then be used as:

	 SELECT group_name, variance3(score)
	 FROM results
	 GROUP BY group_name;

SUPPORT

       Bugs should be reported via the CPAN bug tracker at

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

TO DO

       * Add more and varied cookbook recipes, until we have enough to turn them into a seperate CPAN distribution.

       * Create a series of tests scripts that validate the cookbook recipies.

AUTHOR

       Adam Kennedy <adamk@cpan.org>

COPYRIGHT

       Copyright 2009 Adam Kennedy.

       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.

perl v5.12.1							    2010-01-08						  DBD::SQLite::Cookbook(3)

DBD::SQLite2(3pm)					User Contributed Perl Documentation					 DBD::SQLite2(3pm)

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.hwaci.com/sw/sqlite/.

       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.

       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 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 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 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>

SEE ALSO

       DBI.

perl v5.14.2							    2004-09-10							 DBD::SQLite2(3pm)