In this 
my $name = undef;

# 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;
    }
  }
}
# here, $name will be defined if one of above succeeded

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what is the undef do inside the 
my $rv = $dbh->selectcol_arrayref( $sql, undef, $user );

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In reply to Re: Re(2): (Ovid): uninitialized value in concatenation by mnlight
in thread uninitialized value in concatenation by mnlight

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