SQL info: MySQL Query Error

Time: 2019-1-20 7:50pm
Script: /live/list.php

SQL: SELECT * FROM live_vod_class WHERE parentid= ORDER by classid ASC
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 'ORDER by classid ASC' at line 1
Errno.: 1064