在mysql查询中设置条件

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'

仅当 max_unixtime() - last_reply > 时，我才需要设置latest_conversation last_viewed..

如何在查询中设置 if 语句？

Answer 1

使用 CASE 语句。

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