PHP script to check if a turk worker has done an experiment

exclude_subjects.php

<?php

// sample usage in javascript:

/*

$.ajax({
		type: 'post',
		url: '../exclude_subjects.php',
		data: {"mturk_id": turk.workerId, "tables": JSON.stringify(['exp_1', 'exp_2']), "col_id": "mturk_id"},
		success: function(data)
		{
			if(data=="1")
			{
				// do stuff here to allow subject to continue
			} else {
                                // subject already in database. do stuff to prevent them from doing experiment, like...
				$("#instructions").html('<h3>Sorry, you have already participated in this study or a related study and are not eligible to complete this HIT.</h3>');
			}
		}
	});
*/


// edit this line for database check
include('database_connect.php');

function check_mturk_id($tables, $id) {
	for($i=0; $i < count($tables); $i++){
		$result = mysql_query('SELECT DISTINCT '.mysql_real_escape_string($col_id).' FROM '.mysql_real_escape_string($tables[$i]));
		while($row = mysql_fetch_array($result))
		{
			if($row["mturk_id"] == $id)
			{
				return false;
			}
		}
	}
	
	return true;
}

// get id from POST call
$id = $_POST['mturk_id'];
$col_id = $_POST['col_id'];
$tables = $_POST['tables'];
$tables = json_decode($tables,true);

// check id
$r = check_mturk_id($tables, $id, $col_id);

// echo out TRUE or FALSE
echo $r;
?>

This should sanitize the variables that come in on POST to prevent injections... use at your own risk until that's fixed.

need a file database_connect.php with database connection info.