r2h(..) {
  my $dbh = shift;
  my $table_name = shift;
  my $col_name = shift;
  my $v = shift;
  my $where = shift;
  my @w_conds = @_;
  my $sql = ...
  if($where) {
    $sql .= "($where) and `$col_name`= ?".
   
  } else {
     $sql .= "where `$col_name` = ?";
  }
  ...
}