在mysql查询中进行条件化

Question

'SELECT conversation_id, viewed_on,('max_unixtime().' - last_reply) AS newest_conversation FROM `Conversation_Participant` WHERE `user_id`='.$self->{user}->get('id').' ORDER BY newest_conversation DESC'

我需要在max_unixtime（） - last_reply＆gt;时设置newest_conversation。 last_viewed ..

如何在查询中设置if语句？

Answer 1

使用CASE statement。

...CASE WHEN max_unixtime() - last_reply > last_viewed 
        THEN ('max_unixtime().' - last_reply) 
        ELSE NULL END AS newest_conversation...