my $sql= <<'SQL';
    select
        *
    from mytable
            -- ignore or value
      where (?        or coln1=?)
        and (?        or coln2=?)
        and (?        or coln3=?)
SQL

my $sth= $dbh->prepare( $sql );

my %parameters= (coln2 => 'Hello');

my @parameters;

for my $column (qw(coln1 coln2 coln3) {
    if( exists $parameters{ $column }) {
        # Use this column value
        push @parameters, 0, $parameters{ $column };
    } else {
        # Ignore this column value
        push @parameters, 1, undef;
    };
};

$sth->execute(@parameters);