respondent_id: response_x, response_y, ...

##</code><code>##

respondent_1: 123, 456, 789, 23, 1574, ...
respondent_2: 65, 1893, 2853, 753, ...
etc.

##</code><code>##

count all respondents who gave response x and response y

##</code><code>##

CREATE TABLE `theTable` (
		`response` smallint(5) unsigned NOT NULL default '0',
		`respondent` smallint(5) unsigned NOT NULL default '0',
		PRIMARY KEY (`response`,`respondent`) )
	
##</code><code>##

CREATE TABLE `theTable` ( `respondent` smallint(5) unsigned NOT NULL 
        default '0', `response` smallint(5) unsigned NOT NULL default '0', PRIMARY 
        KEY (`respondent`,`response`), KEY `respondent` (`respondent`), KEY `response` 
        (`response`)
	) 
##</code><code>##

for $i (1 .. $num_responses) {
        $sql = &quot;CREATE TABLE r&quot;.$i.&quot; (respondent smallint unsigned, PRIMARY KEY (respondent))
        $sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr); 
        $sth->execute() or die("Could not execute!" . $sth->errstr); 
        } 
##</code><code>##

 for $i (1 .. $num_responses) { 
        $file = ">response_".$i; 
        open(FILE, $file) or dienice("cannot open file : $_[0] $!"); 
        } 
##</code><code>##

	$sql = "appropriate select statement";
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_2 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute() or die("Could not execute 1!" . $dbh->errstr);
	}
	$count = $sth->fetchrow_array();
	$end_2 = new Benchmark;
	$diff_2 = timediff($end_2, $start_2);

##</code><code>##

	$sql = "appropriate select for response_id_1"
	$sth = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$sql = "appropriate select for response_id_2"
	$stm = $dbh->prepare($sql) or die("Could not prepare!" . $dbh->errstr);
	$start_1 = new Benchmark;
	for $i (0 .. $iterations) {
		$sth->execute() or die("Could not execute 1!" . $dbh->errstr);
		while ($data = $sth->fetchrow_array()) {
			$union{$data} = undef;
		}
		$stm->execute() or die("Could not execute 2!" . $dbh->errstr);
		while ($data = $stm->fetchrow_array()) {
			$isect{$data} = undef if exists $union{$data};
		}
		@isect = keys %isect;
	}
	$end_1 = new Benchmark;
	$diff = timediff($end_1, $start_1);

##</code><code>##

	$start_1 = new Benchmark;
	for $i (0 .. $iterations) {
		$table = "<".$db_dir."/r".$response_id;
	      	open(FILE, $table) or dienice("cannot open file : $table $!");
		while ($data = <FILE>) {
			$union{$data} = undef;
		}
		close(FILE);
		$table = "<".$db_dir."/r6000";
	      	open(FILE, $table) or dienice("cannot open file : $table $!");
		while ($data = <FILE>) {
			$isect{$data} = undef if exists $union{$data};
		}
		close(FILE);
		@isect = keys %isect;
		$response_id++;
	}
	$end_1 = new Benchmark;
	$diff = timediff($end_1, $start_1);