Something
public text v1 · immutable$sql = "SELECT * FROM categories WHERE id IN
(SELECT category_id FROM catrelations WHERE category_id='13')";
$catres = mysql_query($sql) or die(mysql_error());
You have an error in your SQL syntax. Check the manual that corresponds to your MySQL server version for the right syntax to use near 'SELECT category_id FROM catrelations WHERE category_id='13')' a