按順序排列並按組排序

Question

SELECT * FROM(
SELECT c_id, user_id, message, state, time FROM message 
WHERE receive=1 
ORDER BY message_id DESC 
)AS t GROUP BY c_id 

我有mysql語句可以爲用戶提取最後一條消息。

不過，我需要加入用戶表，這樣我就可以取出來了發件人的姓名

LEFT JOIN user ON user.user_id=message.user_id 

如何實現這一目標？

//user 
user_id name 

//conversation 
c_id user_id 

//message 
m_id c_id user_id(sender) receive message state time 

Answer 1

SELECT * FROM (
    SELECT c_id, user_id, message, state, time 
    FROM message 
    WHERE receive=1 
    ORDER BY message_id DESC) AS t 
LEFT JOIN user ON user.user_id=t.user_id 
GROUP BY c_id 

附：檢查user.user_id是否存在。