This code is not working because the sql is returning a '' value and the if statement is seeing it as being true. what can I change so it evaluates the '' as no value returned.

# store subparent for each parent
my %parent_hash = ( 'Father' => 'Mother',
                    'Mother' => 'Father' );

if (exists $parent_hash{$parent}) {
  my $sub_parent = $parent_hash{$parent};

  for my $col ( $parent, $sub_parent ) {
    my $sql = "select $col from Roster where User=?";
    my $rv = $dbh->selectcol_arrayref( $sql, undef, $user);
    if ( @$rv) {  # any rows returned?
      $name = $rv->[0];  # take first one
      last;
    }
  }
}
[download]