我有这个查询:
SELECT customer.cus_id,customer.fname,customer.lname,customer.image, message.message ,message.msg_id,message.from_cus,message.to_cus, message.sent_time
FROM customer
INNER JOIN message ON cus_id=message.from_cus OR cus_id=message.to_cus
WHERE customer.cus_id IN ( 31,26)
AND (
from_cus =25
OR to_cus = 25
)
AND customer.cus_id NOT IN(25)
ORDER BY message.sent_time DESC
GROUP BY customer.cus_id ;
其中31、26是我想要获取其最后消息的客户的cus_id。如果我删除GROUP BY约束,我将根据1和(31,26(客户之间的时间对所有消息进行排序。但添加它会给我这个语法错误
[Error code:1064 SQL state:42000] 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 'GROUP BY customer.cus_id' at line 11
我已禁用ONLY_FULL_GROUP_BY SQL模式。我仍然不知道如何获取最后一条信息。
这不是聚合操作,而是过滤操作。
使用窗口功能:
SELECT cm.* FROM (
SELECT customer.cus_id,customer.fname,customer.lname,customer.image, message.message ,message.msg_id,message.from_cus,message.to_cus, message.sent_time,
ROW_NUMBER() OVER (PARTITION BY customer.cus_id ORDER BY message.sent_time DESC) as seqnum
FROM customer
INNER JOIN message ON cus_id=message.from_cus OR cus_id=message.to_cus
WHERE customer.cus_id IN ( 31,26)
AND (
from_cus =25
OR to_cus = 25
)
AND customer.cus_id NOT IN(25)
) cm
WHERE seqnum = 1
ORDER BY msg_id DESC;
Group by
子句将位于order by
子句之前
SELECT customer.cus_id,customer.fname,customer.lname,customer.image, message.message ,message.msg_id,message.from_cus,message.to_cus, message.sent_time
FROM customer
INNER JOIN message ON cus_id=message.from_cus OR cus_id=message.to_cus
WHERE customer.cus_id IN ( 31,26)
AND (
from_cus =25
OR to_cus = 25
)
AND customer.cus_id NOT IN(25)
GROUP BY customer.cus_id
ORDER BY message.msg_id DESC