You may be able to use SQL::Abstract for that. You may wind up with something like:

my %where_clause = ();
if ( $cgi->param( 'field1' ) ) {
    # obviously, some validation should be here
    $where_clause{ 'field1' } = $cgi->param( 'field1' );
}
# etc.
my $sql = SQL::Abstract->new();
my ( $stmt, @bind ) = $sql->select( 'table',
                                    [ qw( field list ) ],
                                    \%where_clause );
my $sth = $dbh->prepare( $stmt );
$sth->execute( @bind );
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