...
my $form = CGI->new();
my $db_handle = DBI->connect(...);
my @fields = qw(f_1 f_2 f_3 f_4 f_5);
my @query_parts;
foreach my $field (@fields) {
    if ( defined $form->param($field) ) {
        push @query_parts, "$field = " . $db_handle->quote($form->param($field));
    }
}

if ( ! scalar(@query_parts) ) {
    # do something else
    return;
}

my $query = "SELECT * FROM Table_Name WHERE ";
$query .= join " AND ", map { "( $_ )" } @query_parts;