/Library/Perl/5.8.8/CGI/Session/Driver/DBI.pm:
[...]
sub retrieve {
    my $self = shift;
    my ($sid) = @_;
    croak "retrieve(): usage error" unless $sid;


    my $dbh = $self->{Handle};
    my $sth = $dbh->prepare_cached("SELECT a_session FROM " . $self->table_name . " WHERE id=?", undef, 3);
    unless ( $sth ) {
        return $self->set_error( "retrieve(): DBI->prepare failed with error message " . $dbh->errstr );
    }
    $sth->execute( $sid ) or return $self->set_error( "retrieve(): \$sth->execute failed with error message " . $sth->errstr);

    my ($row) = $sth->fetchrow_array();
    return 0 unless $row;
    return $row;
}
[...]