
  CONSTRAINT `fk_inventory_film` FOREIGN KEY (`film_id`) REFERENCES `film` (`film_id`) ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4582 DEFAULT CHARSET=utf8
</pre></blockquote>
<p>

In the above example, note the following:
<ul>
	<li>The <i>PRIMARY</i> key is on <i>inventory_id</i> column, hence contains one column exactly. Since it is UNIQUE, it is certain to have <strong>1</strong> row per key.</li>
	<li>The <i>idx_fk_film_id</i> index is non unique. The INFORMATION_SCHEMA.INNODB_INDEX_STATS table l