#method 1 - Perl intersection using @col arrays
	$sql = "SELECT col_2 FROM theTable WHERE col_1 = ?";
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_1 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute($value_1) or die("Could not execute 1!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			push(@col_1, $data);
		}
		$sth->execute($value_2) or die("Could not execute 2!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			push(@col_2, $data);
		}
		foreach $e (@col_1) { $union{$e} = 1 }
		foreach $e (@col_2) {
		    if ( $union{$e} ) { $isect{$e} = 1 }
		}
		@isect = keys %isect;
	}
	$end_1 = new Benchmark;
	$diff = timediff($end_1, $start_1);

	#method 2 - Perl intersection using 'undef'
	$sql = "SELECT col_2 FROM theTable WHERE col_1 = ?";
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_2 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute($value_1) or die("Could not execute 1!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			$union{$data} = undef;
		}
		$sth->execute($value_2) or die("Could not execute 2!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			$isect{$data} = undef if exists $union{$data};
		}
		@isect = keys %isect;
	}
	$end_2 = new Benchmark;
	$diff = timediff($end_2, $start_2);

	#method 3 - MYSQL
	$sql = "SELECT COUNT(*) FROM theTable A JOIN responses B ON (A.col_2 = B.col_2) WHERE A.col_1 = ? AND B.col_1 = ?";
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_3 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute($value_1, $value_2) or die("Could not execute 1!" . $dbh->errstr);
	}
	$end_3 = new Benchmark;
	$diff = timediff($end_3, $start_3);