DBD-SQLite-SQLcipher/lib/DBD/SQLite.pm

package DBD::SQLite;

use 5.006;
use strict;
use DBI   1.57 ();
use DynaLoader ();

use vars qw($VERSION @ISA);
use vars qw{$err $errstr $drh $sqlite_version};
use vars qw{%COLLATION};

BEGIN {
    $VERSION = '1.26_02';
    @ISA     = 'DynaLoader';

    # Initialize errors
    $err     = undef;
    $errstr  = undef;

    # Driver singleton
    $drh = undef;

    # sqlite_version cache
    $sqlite_version = undef;

}

__PACKAGE__->bootstrap($VERSION);

%COLLATION = (
  perl       => sub { $_[0] cmp $_[1] },
  perllocale => sub { use locale; $_[0] cmp $_[1] },
 );


my $methods_are_installed;

sub driver {
    return $drh if $drh;

    if (!$methods_are_installed && $DBI::VERSION >= 1.608) {
        DBI->setup_driver('DBD::SQLite');

        DBD::SQLite::db->install_method('sqlite_last_insert_rowid');
        DBD::SQLite::db->install_method('sqlite_busy_timeout');
        DBD::SQLite::db->install_method('sqlite_create_function');
        DBD::SQLite::db->install_method('sqlite_create_aggregate');
        DBD::SQLite::db->install_method('sqlite_create_collation');
        DBD::SQLite::db->install_method('sqlite_collation_needed');
        DBD::SQLite::db->install_method('sqlite_progress_handler');
        DBD::SQLite::db->install_method('sqlite_commit_hook');
        DBD::SQLite::db->install_method('sqlite_rollback_hook');
        DBD::SQLite::db->install_method('sqlite_update_hook');
        DBD::SQLite::db->install_method('sqlite_set_authorizer');
        DBD::SQLite::db->install_method('sqlite_backup_from_file');
        DBD::SQLite::db->install_method('sqlite_backup_to_file');
        DBD::SQLite::db->install_method('sqlite_enable_load_extension');
        $methods_are_installed++;
    }

    $drh = DBI::_new_drh( "$_[0]::dr", {
        Name        => 'SQLite',
        Version     => $VERSION,
        Attribution => 'DBD::SQLite by Matt Sergeant et al',
    } );
    return $drh;
}

sub CLONE {
    undef $drh;
}

package DBD::SQLite::dr;

sub connect {
    my ($drh, $dbname, $user, $auth, $attr) = @_;

    # Default PrintWarn to the value of $^W
    unless ( defined $attr->{PrintWarn} ) {
        $attr->{PrintWarn} = $^W ? 1 : 0;
    }

    my $dbh = DBI::_new_dbh( $drh, {
        Name => $dbname,
    } );

    my $real = $dbname;
    if ( $dbname =~ /=/ ) {
        foreach my $attrib ( split(/;/, $dbname) ) {
            my ($key, $value) = split(/=/, $attrib, 2);
            if ( $key eq 'dbname' ) {
                $real = $value;
            } else {
                $attr->{$key} = $value;
            }
        }
    }

    # To avoid unicode and long file name problems on Windows,
    # convert to the shortname if the file (or parent directory) exists.
    if ( $^O =~ /MSWin32/ and $real ne ':memory:' ) {
        require Win32;
        require File::Basename;
        my ($file, $dir, $suffix) = File::Basename::fileparse($real);
        my $short = Win32::GetShortPathName($real);
        if ( $short && -f $short ) {
            # Existing files will work directly.
            $real = $short;
        } elsif ( -d $dir ) {
            # We are creating a new file.
            # Does the directory it's in at least exist?
            $real = join '', grep { defined } Win32::GetShortPathName($dir), $file, $suffix;
        } else {
            # SQLite can't do mkpath anyway.
            # So let it go through as it and fail.
        }
    }

    # Hand off to the actual login function
    DBD::SQLite::db::_login($dbh, $real, $user, $auth) or return undef;

    # Register the on-demand collation installer
    $DBI::VERSION >= 1.608 
      ? $dbh->sqlite_collation_needed(\&install_collation)
      : $dbh->func(\&install_collation, "collation_needed");

    # Register the REGEXP function 
    $DBI::VERSION >= 1.608 
      ? $dbh->sqlite_create_function("REGEXP", 2, \&regexp)
      : $dbh->func("REGEXP", 2, \&regexp, "create_function");


    # HACK: Since PrintWarn = 0 doesn't seem to actually prevent warnings
    # in DBD::SQLite we set Warn to false if PrintWarn is false.
    unless ( $attr->{PrintWarn} ) {
        $attr->{Warn} = 0;
    }

    return $dbh;
}


sub install_collation {
  my ($dbh, $collation_name) = @_;
  my $collation = $DBD::SQLite::COLLATION{$collation_name}
    or die "can't install, unknown collation : $collation_name";
  $DBI::VERSION >= 1.608 
      ? $dbh->sqlite_create_collation($collation_name => $collation)
      : $dbh->func($collation_name => $collation, "create_collation");
}

# default implementation for sqlite 'REGEXP' infix operator.
# Note : args are reversed, i.e. "a REGEXP b" calls REGEXP(b, a)
# (see http://www.sqlite.org/vtab.html#xfindfunction)
sub regexp { 
  use locale;
  return scalar($_[1] =~ $_[0]);
}


package DBD::SQLite::db;

sub prepare {
    my $dbh = shift;
    my $sql = shift;

    my $sth = DBI::_new_sth( $dbh, {
        Statement => $sql,
    } );

    DBD::SQLite::st::_prepare($sth, $sql, @_) or return undef;

    return $sth;
}

sub _get_version {
    return ( DBD::SQLite::db::FETCH($_[0], 'sqlite_version') );
}

my %info = (
    17 => 'SQLite',       # SQL_DBMS_NAME
    18 => \&_get_version, # SQL_DBMS_VER
    29 => '"',            # SQL_IDENTIFIER_QUOTE_CHAR
);

sub get_info {
    my($dbh, $info_type) = @_;
    my $v = $info{int($info_type)};
    $v = $v->($dbh) if ref $v eq 'CODE';
    return $v;
}

sub _attached_database_list {
    my $dbh = shift;
    my @attached;

    my $sth_databases = $dbh->prepare( 'PRAGMA database_list' );
    $sth_databases->execute;
    while ( my $db_info = $sth_databases->fetchrow_hashref ) {
        push @attached, $db_info->{name} if $db_info->{seq} >= 2;
    }
    return @attached;
}

# SQL/CLI (ISO/IEC JTC 1/SC 32 N 0595), 6.63 Tables
# Based on DBD::Oracle's
# See also http://www.ch-werner.de/sqliteodbc/html/sqlite3odbc_8c.html#a213
sub table_info {
    my ($dbh, $cat_val, $sch_val, $tbl_val, $typ_val) = @_;

    my @where = ();
    my $sql;
    if (  defined($cat_val) && $cat_val eq '%'
       && defined($sch_val) && $sch_val eq ''
       && defined($tbl_val) && $tbl_val eq '')  { # Rule 19a
            $sql = <<'END_SQL';
SELECT NULL TABLE_CAT
     , NULL TABLE_SCHEM
     , NULL TABLE_NAME
     , NULL TABLE_TYPE
     , NULL REMARKS
END_SQL
    }
    elsif (  defined($cat_val) && $cat_val eq ''
          && defined($sch_val) && $sch_val eq '%'
          && defined($tbl_val) && $tbl_val eq '') { # Rule 19b
            $sql = <<'END_SQL';
SELECT NULL      TABLE_CAT
     , t.tn      TABLE_SCHEM
     , NULL      TABLE_NAME
     , NULL      TABLE_TYPE
     , NULL      REMARKS
FROM (
     SELECT 'main' tn
     UNION SELECT 'temp' tn
END_SQL
            for my $db_name (_attached_database_list($dbh)) {
                $sql .= "     UNION SELECT '$db_name' tn\n";
            }
            $sql .= ") t\n";
    }
    elsif (  defined($cat_val) && $cat_val eq ''
          && defined($sch_val) && $sch_val eq ''
          && defined($tbl_val) && $tbl_val eq ''
          && defined($typ_val) && $typ_val eq '%') { # Rule 19c
            $sql = <<'END_SQL';
SELECT NULL TABLE_CAT
     , NULL TABLE_SCHEM
     , NULL TABLE_NAME
     , t.tt TABLE_TYPE
     , NULL REMARKS
FROM (
     SELECT 'TABLE' tt                  UNION
     SELECT 'VIEW' tt                   UNION
     SELECT 'LOCAL TEMPORARY' tt
) t
ORDER BY TABLE_TYPE
END_SQL
    }
    else {
            $sql = <<'END_SQL';
SELECT *
FROM
(
SELECT NULL         TABLE_CAT
     ,              TABLE_SCHEM
     , tbl_name     TABLE_NAME
     ,              TABLE_TYPE
     , NULL         REMARKS
     , sql          sqlite_sql
FROM (
    SELECT 'main' TABLE_SCHEM, tbl_name, upper(type) TABLE_TYPE, sql
    FROM sqlite_master
    WHERE type IN ( 'table','view')
UNION ALL
    SELECT 'temp' TABLE_SCHEM, tbl_name, 'LOCAL TEMPORARY' TABLE_TYPE, sql
    FROM sqlite_temp_master
    WHERE type IN ( 'table','view')
END_SQL

            for my $db_name (_attached_database_list($dbh)) {
                    $sql .= <<"END_SQL";
UNION ALL
    SELECT '$db_name' TABLE_SCHEM, tbl_name, upper(type) TABLE_TYPE, sql
    FROM "$db_name".sqlite_master
    WHERE type IN ('table','view')
END_SQL
            }

            $sql .= <<'END_SQL';
UNION ALL
    SELECT 'main' TABLE_SCHEM, 'sqlite_master'      tbl_name, 'SYSTEM TABLE' TABLE_TYPE, NULL sql
UNION ALL
    SELECT 'temp' TABLE_SCHEM, 'sqlite_temp_master' tbl_name, 'SYSTEM TABLE' TABLE_TYPE, NULL sql
)
)
END_SQL
            if ( defined $sch_val ) {
                    push @where, "TABLE_SCHEM LIKE '$sch_val'";
            }
            if ( defined $tbl_val ) {
                    push @where, "TABLE_NAME LIKE '$tbl_val'";
            }
            if ( defined $typ_val ) {
                    my $table_type_list;
                    $typ_val =~ s/^\s+//;
                    $typ_val =~ s/\s+$//;
                    my @ttype_list = split (/\s*,\s*/, $typ_val);
                    foreach my $table_type (@ttype_list) {
                            if ($table_type !~ /^'.*'$/) {
                                    $table_type = "'" . $table_type . "'";
                            }
                            $table_type_list = join(", ", @ttype_list);
                    }
                    push @where, "TABLE_TYPE IN (\U$table_type_list)" if $table_type_list;
            }
            $sql .= ' WHERE ' . join("\n   AND ", @where ) . "\n" if @where;
            $sql .= " ORDER BY TABLE_TYPE, TABLE_SCHEM, TABLE_NAME\n";
    }
    my $sth = $dbh->prepare($sql) or return undef;
    $sth->execute or return undef;
    $sth;
}

sub primary_key_info {
    my($dbh, $catalog, $schema, $table) = @_;

    # This is a hack but much simpler than using pragma index_list etc
    # also the pragma doesn't list 'INTEGER PRIMARY KEY' autoinc PKs!
    my @pk_info;
    my $sth_tables = $dbh->table_info($catalog, $schema, $table, '');
    while ( my $row = $sth_tables->fetchrow_hashref ) {
        my $sql = $row->{sqlite_sql} or next;
        next unless $sql =~ /(.*?)\s*PRIMARY\s+KEY\s*(?:\(\s*(.*?)\s*\))?/si;
        my @pk = split /\s*,\s*/, $2 || '';
        unless ( @pk ) {
            my $prefix = $1;
            $prefix =~ s/.*create\s+table\s+.*?\(\s*//si;
            $prefix = (split /\s*,\s*/, $prefix)[-1];
            @pk = (split /\s+/, $prefix)[0]; # take first word as name
        }
        my $key_seq = 0;
        foreach my $pk_field (@pk) {
            push @pk_info, {
                TABLE_SCHEM => $row->{TABLE_SCHEM},
                TABLE_NAME  => $row->{TABLE_NAME},
                COLUMN_NAME => $pk_field,
                KEY_SEQ     => ++$key_seq,
                PK_NAME     => 'PRIMARY KEY',
            };
        }
    }

    my $sponge = DBI->connect("DBI:Sponge:", '','')
        or return $dbh->DBI::set_err($DBI::err, "DBI::Sponge: $DBI::errstr");
    my @names = qw(TABLE_CAT TABLE_SCHEM TABLE_NAME COLUMN_NAME KEY_SEQ PK_NAME);
    my $sth = $sponge->prepare( "column_info $table", {
        rows          => [ map { [ @{$_}{@names} ] } @pk_info ],
        NUM_OF_FIELDS => scalar @names,
        NAME          => \@names,
    }) or return $dbh->DBI::set_err(
        $sponge->err(),
        $sponge->errstr()
    );
    return $sth;
}

sub type_info_all {
    return; # XXX code just copied from DBD::Oracle, not yet thought about
#    return [
#        {
#            TYPE_NAME          =>  0,
#            DATA_TYPE          =>  1,
#            COLUMN_SIZE        =>  2,
#            LITERAL_PREFIX     =>  3,
#            LITERAL_SUFFIX     =>  4,
#            CREATE_PARAMS      =>  5,
#            NULLABLE           =>  6,
#            CASE_SENSITIVE     =>  7,
#            SEARCHABLE         =>  8,
#            UNSIGNED_ATTRIBUTE =>  9,
#            FIXED_PREC_SCALE   => 10,
#            AUTO_UNIQUE_VALUE  => 11,
#            LOCAL_TYPE_NAME    => 12,
#            MINIMUM_SCALE      => 13,
#            MAXIMUM_SCALE      => 14,
#            SQL_DATA_TYPE      => 15,
#            SQL_DATETIME_SUB   => 16,
#            NUM_PREC_RADIX     => 17,
#        },
#        [ 'CHAR', 1, 255, '\'', '\'', 'max length', 1, 1, 3,
#            undef, '0', '0', undef, undef, undef, 1, undef, undef
#        ],
#        [ 'NUMBER', 3, 38, undef, undef, 'precision,scale', 1, '0', 3,
#            '0', '0', '0', undef, '0', 38, 3, undef, 10
#        ],
#        [ 'DOUBLE', 8, 15, undef, undef, undef, 1, '0', 3,
#            '0', '0', '0', undef, undef, undef, 8, undef, 10
#        ],
#        [ 'DATE', 9, 19, '\'', '\'', undef, 1, '0', 3,
#            undef, '0', '0', undef, '0', '0', 11, undef, undef
#        ],
#        [ 'VARCHAR', 12, 1024*1024, '\'', '\'', 'max length', 1, 1, 3,
#            undef, '0', '0', undef, undef, undef, 12, undef, undef
#        ]
#    ];
}

my @COLUMN_INFO = qw(
    TABLE_CAT
    TABLE_SCHEM
    TABLE_NAME
    COLUMN_NAME
    DATA_TYPE
    TYPE_NAME
    COLUMN_SIZE
    BUFFER_LENGTH
    DECIMAL_DIGITS
    NUM_PREC_RADIX
    NULLABLE
    REMARKS
    COLUMN_DEF
    SQL_DATA_TYPE
    SQL_DATETIME_SUB
    CHAR_OCTET_LENGTH
    ORDINAL_POSITION
    IS_NULLABLE
);

# Taken from Fey::Loader::SQLite
sub column_info {
    my($dbh, $catalog, $schema, $table, $column) = @_;

    if ( defined $column and $column eq '%' ) {
        $column = undef;
    }

    my @cols        = ();
    my $position    = 0;
    my $sth_columns = $dbh->prepare("PRAGMA table_info('$table')");
    $sth_columns->execute;
    while ( my $col_info = $sth_columns->fetchrow_hashref ) {
        $position++;
        next if defined $column && $column ne $col_info->{name};

        my %col = (
            TABLE_NAME       => $table,
            COLUMN_NAME      => $col_info->{name},
            ORDINAL_POSITION => $position,
        );

        my $type = $col_info->{type};
        if ( $type =~ s/(\w+)\((\d+)(?:,(\d+))?\)/$1/ ) {
            $col{COLUMN_SIZE}    = $2;
            $col{DECIMAL_DIGITS} = $3;
        }

        $col{TYPE_NAME} = $type;

        if ( defined $col_info->{dflt_value} ) {
            $col{COLUMN_DEF} = $col_info->{dflt_value}
        }

        if ( $col_info->{notnull} ) {
            $col{NULLABLE}    = 0;
            $col{IS_NULLABLE} = 'NO';
        } else {
            $col{NULLABLE}    = 1;
            $col{IS_NULLABLE} = 'YES';
        }

        foreach my $key ( @COLUMN_INFO ) {
            next if exists $col{$key};
            $col{$key} = undef;
        }

        push @cols, \%col;
    }
    $sth_columns->finish;

    my $sponge = DBI->connect("DBI:Sponge:", '','')
        or return $dbh->DBI::set_err($DBI::err, "DBI::Sponge: $DBI::errstr");
    my $sth = $sponge->prepare( "column_info $table", {
        rows          => [ map { [ @{$_}{@COLUMN_INFO} ] } @cols ],
        NUM_OF_FIELDS => scalar @COLUMN_INFO,
        NAME          => [ @COLUMN_INFO ],
    } ) or return $dbh->DBI::set_err(
        $sponge->err,
        $sponge->errstr,
    );

    return $sth;
}

1;

__END__

=pod

=head1 NAME

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

=head1 SYNOPSIS

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

=head1 DESCRIPTION

SQLite is a public domain file-based relational database engine that
you can find at L<http://www.sqlite.org/>.

B<DBD::SQLite> is a Perl DBI driver for SQLite, that 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 B<nothing>
else.

SQLite supports the following features:

=over 4

=item Implements a large subset of SQL92

See L<http://www.sqlite.org/lang.html> for details.

=item 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 L<DBD::CSV>.

=item Atomic commit and rollback

Yes, B<DBD::SQLite> is small and light, but it supports full transactions!

=item Extensible

User-defined aggregate or regular functions can be registered with the
SQL parser.

=back

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 L<DBI> for details
on how to use DBI itself.

=head1 CONFORMANCE WITH DBI SPECIFICATION

The API works like every DBI module does. Please see L<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.

=head1 DRIVER PRIVATE ATTRIBUTES

=head2 Database Handle Attributes

=over 4

=item sqlite_version

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

=item unicode

If set to a true value, B<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
L<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
L<http://www.sqlite.org/datatype3.html>), if you want to retain
blob-style behavior for B<some> columns under C<< $dbh->{unicode} = 1
>> (say, to store images in the database), you have to state so
explicitly using the 3-argument form of L<DBI/bind_param> 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 C<BLOB> in the DDL is B<not> sufficient.

=back

=head1 DRIVER PRIVATE METHODS

The following methods can be called via the func() method with a little tweak, but the use of func() method is now discouraged by the L<DBI> author for various reasons (see L<DBI's document|http://search.cpan.org/dist/DBI/lib/DBI/DBD.pm#Using_install_method()_to_expose_driver-private_methods> for details). So, if you're using L<DBI> >= 1.608, use these C<sqlite_> methods. If you need to use an older L<DBI>, you can call these like this:

  $dbh->func( ..., "(method name without sqlite_ prefix)" );

=head2 $dbh->sqlite_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 L<DBI> last_insert_id
method instead. The usage of this is:

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

Running C<$h-E<gt>last_insert_id("","","","")> is the equivalent of running
C<$dbh-E<gt>sqlite_last_insert_rowid()> directly.

=head2 $dbh->sqlite_busy_timeout()

Retrieve the current busy timeout.

=head2 $dbh->sqlite_busy_timeout( $ms )

Set the current busy timeout. The timeout is in milliseconds.

=head2 $dbh->sqlite_create_function( $name, $argc, $code_ref )

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

=over

=item $name

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

=item $argc

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

=item $code_ref

This should be a reference to the function's implementation.

=back

For example, here is how to define a now() function which returns the
current number of seconds since the epoch:

  $dbh->sqlite_create_function( 'now', 0, sub { return time } );

After this, it could be use from SQL as:

  INSERT INTO mytable ( now() );


=head3 REGEXP function

SQLite includes syntactic support for an infix operator 'REGEXP', but
without any implementation. The C<DBD::SQLite> driver
automatically registers an implementation that performs standard
perl regular expression matching, using current locale. So for example
you can search for words starting with an 'A' with a query like

  SELECT * from table WHERE column REGEXP '\bA\w+'

If you want case-insensitive searching, use perl regex flags, like this :

  SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'

The default REGEXP implementation can be overriden through the
C<create_function> API described above.

Note that regexp matching will B<not> use SQLite indices, but will iterate
over all rows, so it could be quite costly in terms of performance.


=head2 $dbh->sqlite_create_collation( $name, $code_ref )

This method manually registers a new function which will be useable in an SQL
query as a COLLATE option for sorting. Such functions can also be registered
automatically on demand: see section L</"COLLATION FUNCTIONS"> below.

The method's parameters are:

=over

=item $name

The name of the function exposed to SQL.

=item $code_ref

Reference to the function's implementation.
The driver will check that this is a proper sorting function.

=back


=head2 $dbh->sqlite_collation_needed( $code_ref )

This method manually registers a callback function that will
be invoked whenever an undefined collation sequence is required.
The callback is invoked as 

  $code_ref->($dbh, $collation_name)

and should register the desired collation using 
L</"sqlite_create_collation">. 

An initial callback is already registered by C<DBD::SQLite>,
so for most common cases it will be simpler to just
add your collation sequences in the C<%DBD::SQLite::COLLATION>
hash (see section L</"COLLATION FUNCTIONS"> below).


=head2 $dbh->sqlite_create_aggregate( $name, $argc, $pkg )

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

=over

=item $name

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

=item $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.

=item $pkg

This is the package which implements the aggregator interface.

=back

The aggregator interface consists of defining three methods:

=over

=item 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.

=item step(@_)

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

=item 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().

=back

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->sqlite_create_aggregate( "variance", 1, 'variance' );

The aggregate function can then be used as:

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

For more examples, see the L<DBD::SQLite::Cookbook>.

=head2 $dbh->sqlite_progress_handler( $n_opcodes, $code_ref )

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:

=over

=item $n_opcodes

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

=item $code_ref

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 C<undef> if you want to unregister a previous
progress handler.

=back

=head2 $dbh->sqlite_commit_hook( $code_ref )

This method registers a callback function to be invoked whenever a
transaction is committed. Any callback set by a previous call to
C<sqlite_commit_hook> is overridden. A reference to the previous
callback (if any) is returned.  Registering an C<undef> disables the
callback.

When the commit hook callback returns zero, the commit operation is
allowed to continue normally. If the callback returns non-zero, then
the commit is converted into a rollback (in that case, any attempt to
I<explicitly> call C<< $dbh->rollback() >> afterwards would yield an
error).

=head2 $dbh->sqlite_rollback_hook( $code_ref )

This method registers a callback function to be invoked whenever a
transaction is rolled back. Any callback set by a previous call to
C<sqlite_rollback_hook> is overridden. A reference to the previous
callback (if any) is returned.  Registering an C<undef> disables the
callback.


=head2 $dbh->sqlite_update_hook( $code_ref )

This method registers a callback function to be invoked whenever a row
is updated, inserted or deleted. Any callback set by a previous call to
C<sqlite_update_hook> is overridden. A reference to the previous
callback (if any) is returned.  Registering an C<undef> disables the
callback.

The callback will be called as

  $code_ref->($action_code, $database, $table, $rowid)

where

=over

=item $action_code

is an integer equal to either C<DBD::SQLite::INSERT>,
C<DBD::SQLite::DELETE> or C<DBD::SQLite::UPDATE>
(see L</"Action Codes">);

=item $database

is the name of the database containing the affected row;

=item $table

is the name of the table containing the affected row;

=item $rowid

is the unique 64-bit signed integer key of the affected row within that table.

=back


=head2 $dbh->sqlite_set_authorizer( $code_ref )

This method registers an authorizer callback to be invoked whenever
SQL statements are being compiled by the L<DBI/prepare> method.  The
authorizer callback should return C<DBD::SQLite::OK> to allow the
action, C<DBD::SQLite::IGNORE> to disallow the specific action but
allow the SQL statement to continue to be compiled, or
C<DBD::SQLite::DENY> to cause the entire SQL statement to be rejected
with an error. If the authorizer callback returns any other value,
then then C<prepare> call that triggered the authorizer will fail with
an error message.

An authorizer is used when preparing SQL statements from an untrusted
source, to ensure that the SQL statements do not try to access data
they are not allowed to see, or that they do not try to execute
malicious statements that damage the database. For example, an
application may allow a user to enter arbitrary SQL queries for
evaluation by a database. But the application does not want the user
to be able to make arbitrary changes to the database. An authorizer
could then be put in place while the user-entered SQL is being
prepared that disallows everything except SELECT statements.

The callback will be called as

  $code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)

where

=over

=item $action_code

is an integer that specifies what action is being authorized
(see L</"Action Codes">).

=item $string1, $string2

are strings that depend on the action code
(see L</"Action Codes">).

=item $database

is the name of the database (C<main>, C<temp>, etc.) if applicable.

=item $trigger_or_view

is the name of the inner-most trigger or view that is responsible for
the access attempt, or C<undef> if this access attempt is directly from
top-level SQL code.

=back



=head2 $dbh->sqlite_backup_from_file( $filename )

This method accesses the SQLite Online Backup API, and will take a backup of
the named database file, copying it to, and overwriting, your current database
connection. This can be particularly handy if your current connection is to the
special :memory: database, and you wish to populate it from an existing DB.

=head2 $dbh->sqlite_backup_to_file( $filename )

This method accesses the SQLite Online Backup API, and will take a backup of
the currently connected database, and write it out to the named file.

=head2 $dbh->sqlite_enable_load_extension( $bool )

Calling this method with a true value enables loading (external)
sqlite3 extensions. After the call, you can load extensions like this:

  $dbh->sqlite_enable_load_extension(1);
  $sth = $dbh->prepare("select load_extension('libsqlitefunctions.so')")
  or die "Cannot prepare: " . $dbh->errstr();


=head1 DRIVER CONSTANTS

A subset of SQLite C constants are made available to Perl,
because they may be needed when writing
hooks or authorizer callbacks. For accessing such constants, 
the C<DBD::Sqlite> module must be explicitly C<use>d at compile
time. For example, an authorizer that forbids any
DELETE operation would be written as follows :

  use DBD::SQLite;
  $dbh->sqlite_set_authorizer(sub {
    my $action_code = shift;
    return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
                                               : DBD::SQLite::OK;
  });

The list of constants implemented in C<DBD::SQLite> is given 
below; more information can be found ad 
at L<http://www.sqlite.org/c3ref/constlist.html>.

=head2 Authorizer Return Codes

  OK
  DENY
  IGNORE

=head2 Action Codes

The L</set_authorizer> method registers a callback function that is
invoked to authorize certain SQL statement actions. The first
parameter to the callback is an integer code that specifies what
action is being authorized. The second and third parameters to the 
callback are strings, the meaning of which varies according to the 
action code. Below is the list of action codes, together with their
associated strings.

  # constant              string1         string2
  # ========              =======         =======
  CREATE_INDEX            Index Name      Table Name
  CREATE_TABLE            Table Name      undef
  CREATE_TEMP_INDEX       Index Name      Table Name
  CREATE_TEMP_TABLE       Table Name      undef
  CREATE_TEMP_TRIGGER     Trigger Name    Table Name
  CREATE_TEMP_VIEW        View Name       undef
  CREATE_TRIGGER          Trigger Name    Table Name
  CREATE_VIEW             View Name       undef
  DELETE                  Table Name      undef
  DROP_INDEX              Index Name      Table Name
  DROP_TABLE              Table Name      undef
  DROP_TEMP_INDEX         Index Name      Table Name
  DROP_TEMP_TABLE         Table Name      undef
  DROP_TEMP_TRIGGER       Trigger Name    Table Name
  DROP_TEMP_VIEW          View Name       undef
  DROP_TRIGGER            Trigger Name    Table Name
  DROP_VIEW               View Name       undef
  INSERT                  Table Name      undef
  PRAGMA                  Pragma Name     1st arg or undef
  READ                    Table Name      Column Name
  SELECT                  undef           undef
  TRANSACTION             Operation       undef
  UPDATE                  Table Name      Column Name
  ATTACH                  Filename        undef
  DETACH                  Database Name   undef
  ALTER_TABLE             Database Name   Table Name
  REINDEX                 Index Name      undef
  ANALYZE                 Table Name      undef
  CREATE_VTABLE           Table Name      Module Name
  DROP_VTABLE             Table Name      Module Name
  FUNCTION                undef           Function Name
  SAVEPOINT               Operation       Savepoint Name


=head1 COLLATION FUNCTIONS

=head2 Definition

SQLite v3 provides the ability for users to supply arbitrary
comparison functions, known as user-defined "collation sequences" or
"collating functions", to be used for comparing two text values.
L<http://www.sqlite.org/datatype3.html#collation>
explains how collations are used in various SQL expressions.

=head2 Builtin collation sequences

The following collation sequences are builtin within SQLite :

=over

=item B<BINARY>

Compares string data using memcmp(), regardless of text encoding.

=item B<NOCASE>

The same as binary, except the 26 upper case characters of ASCII are
folded to their lower case equivalents before the comparison is
performed. Note that only ASCII characters are case folded. SQLite
does not attempt to do full UTF case folding due to the size of the
tables required.

=item B<RTRIM>

The same as binary, except that trailing space characters are ignored.

=back

In addition, C<DBD::SQLite> automatically installs the 
following collation sequences :

=over

=item B<perl>

corresponds to the Perl C<cmp> operator

=item B<perllocale>

Perl C<cmp> operator, in a context where C<use locale> is activated.

=back

=head2 Usage

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

=head2 Unicode handling

If the attribute C<< $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
C<unicode> attribute is set B<before> the first call to
a perl collation sequence . 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,
      }
  );


=head2 Adding user-defined collation

The native SQLite API for adding user-defined collations is 
exposed through methods L</"sqlite_create_collation"> and
L</"sqlite_collation_needed">.

To avoid calling these functions every time a C<$dbh> handle is
created, C<DBD::SQLite> offers a simpler interface through the
C<%DBD::SQLite::COLLATION> hash : just insert your own
collation functions in that hash, and whenever an unknown
collation name is encountered in SQL, the appropriate collation
function will be loaded on demand from the hash. For example,
here is a way to sort text values regardless of their accented
characters :

  use DBD::SQLite;
  $DBD::SQLite::COLLATION{no_accents} = sub {
    my ( $a, $b ) = map lc, @_;
    tr[<5B><><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD><EFBFBD>]
      [aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
    $a cmp $b;
  };
  my $dbh  = DBI->connect("dbi:SQLite:dbname=dbfile");
  my $sql  = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
  my $rows = $dbh->selectall_arrayref($sql);


The builtin C<perl> or C<perllocale> collations are also in
the same hash and therefore could be overridden if needed.


=head1 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

=head1 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 L<DBI::Shell> module. Just type:

  dbish dbi:SQLite:foo.db

On the command line to access the file F<foo.db>.

Alternatively you can install SQLite from the link above without conflicting
with B<DBD::SQLite> and use the supplied C<sqlite> command line tool.

=head1 FUNCTIONS AND BIND PARAMETERS

As of this writing, a SQL that compares a return value of a function with a numeric bind value like this doesn't work as you might expect.

  my $sth = $dbh->prepare(q{
    SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
  });
  $sth->execute(5);

This is because DBD::SQLite assumes that all the bind values are text (and should be quoted) by default. Thus the above statement becomes like this while executing:

  SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";

There are two workarounds for this.

=over 4

=item Use bind_param() explicitly

As shown above in the C<BLOB> section, you can always use C<bind_param()> to tell the type of a bind value.

  use DBI qw(:sql_types);  # Don't forget this
  
  my $sth = $dbh->prepare(q{
    SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
  });
  $sth->bind_param(1, 5, SQL_INTEGER);
  $sth->execute();

=item Add zero to make it a number

This is somewhat weird, but works anyway.

  my $sth = $dbh->prepare(q{
    SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
  });
  $sth->execute(5);

=back

=head1 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 (L<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.

=head1 TO DO

The following items remain to be done.

=head2 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.

=head2 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.

=head2 Stream API for Blobs

Reading/writing into blobs using C<sqlite2_blob_open> / C<sqlite2_blob_close>.

=head1 SUPPORT

Bugs should be reported via the CPAN bug tracker at

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

=head1 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.

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

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

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

Switch tests to L<Test::More> to support more advanced testing behaviours

=head1 AUTHOR

Matt Sergeant E<lt>matt@sergeant.orgE<gt>

Francis J. Lacoste E<lt>flacoste@logreport.orgE<gt>

Wolfgang Sourdeau E<lt>wolfgang@logreport.orgE<gt>

Adam Kennedy E<lt>adamk@cpan.orgE<gt>

Max Maischein E<lt>corion@cpan.orgE<gt>

Laurent Dami E<lt>dami@cpan.orgE<gt>

=head1 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 L<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.

=cut