Question

这是我的简单消息DB

id | from_id | to_id | created_at

所以我有查询获取对话框列表（这里我只得到结果的coll - 最后一条带有collocutor的消息的最后一个id）：

SELECT IF(to_id = #{id}, from_id, to_id) as coll,
       LEAST(from_id,to_id), 
       GREATEST(from_id, to_id), 
       MAX(created_at), 
       MAX(id) FROM `messages`  
WHERE LEAST(from_id,to_id) = #{id} or GREATEST(from_id, to_id) = #{id}
GROUP BY LEAST(from_id,to_id), GREATEST(from_id, to_id)
ORDER BY MAX(created_at) DESC

从这个查询中我得到了每个collocutors的最后消息列表。现在我需要获得所有最后的消息id与每个collocutors，其中最后一条消息是从collocutor到ME。第一个想法是通过MAX（id）加入消息表。所以代码诞生了：

SELECT IF( m1.to_id = #{id}, m1.from_id, m1.to_id ) AS coll,
       LEAST( m1.from_id, m1.to_id ) ,       
       GREATEST( m1.from_id, m1.to_id ) , 
       MAX( m1.created_at ) , 
       MAX( m1.id )
FROM  `messages` AS m1 
INNER  JOIN messages AS m2 on m2.id = MAX( m1.id )
WHERE  (
         LEAST( m1.from_id, m1.to_id ) = #{id}
         OR GREATEST( m1.from_id, m1.to_id ) = #{id}
       )
       AND
       m2.from <> #{id}
GROUP BY LEAST( m1.from_id, m1.to_id ) , GREATEST( m1.from_id, m1.to_id ) 
ORDER BY MAX( m1.created_at ) DESC

但是上升＃1111错误。第二个想法是“嗯，实际上我需要将第二个消息表连接到第一个查询的结果”。所以现在出生的猴子代码：

Select * from (SELECT IF(to_id = #{id}, from_id, to_id) as coll,
       LEAST(from_id,to_id), 
       GREATEST(from_id, to_id), 
       MAX(created_at), 
       MAX(id) as max_id
FROM `messages`  
WHERE LEAST(from_id,to_id) = #{id} or GREATEST(from_id, to_id) = #{id}
GROUP BY LEAST(from_id,to_id), GREATEST(from_id, to_id)
ORDER BY MAX(created_at) DESC) m1
LEFT JOIN messages as m2 on m1.max_id = m2.id
WHERE to_id =#{id}

所以，那是有效的。但是优化呢？有任何想法吗？

MySQL消息模型查询+最后一组

0 个答案: