function get_prereq_items($prereq_id)
{
    global $wpdb;
    $prereq_items_table_name = get_prereq_items_table_name();
    $items = $wpdb->get_results("SELECT item_id FROM " . $prereq_items_table_name . " WHERE prereq_id = " . $prereq_id);
    return $items;
}
function build_prereq_item_sql()
{
    $table_name = get_prereq_items_table_name();
    $sql = 'CREATE TABLE `' . $table_name . '` (
    `prereq_id` int(10) NOT NULL,
    `item_id` int(10) NOT NULL,
    PRIMARY KEY (prereq_id, item_id),
    FOREIGN KEY (prereq_id) REFERENCES ' . get_prereq_table_name() . '(id) ON DELETE CASCADE,

    FOREIGN KEY (item_id) REFERENCES ' . get_items_table_name() . '(id) ON DELETE CASCADE
    )ENGINE=MyISAM DEFAULT CHARSET=latin1;';
    return $sql;
}