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问题描述
我正在尝试更新名称为 John 的最新记录(John 有多个记录但 ID 不同)，但我似乎处于绑定状态.我的查询有什么问题?
I'm trying to update the latest record where name is John (John has multiple records but different ID) but I seem to be in a bind. What's wrong with my query?
UPDATE messages_tbl SET is_unread=1
WHERE ReceiveTime = (SELECT MAX(ReceiveTime) FROM messages_tbl WHERE name='John')
有没有更好的方法来做这样的事情?
Is there a better way to do something like this?
推荐答案
可以同时加入，根据条件进行更新.
You can join both and perform update based on the condition.
UPDATE messages a
INNER JOIN
(
SELECT name , MAX(ReceiveTime) max_time
FROM messages
GROUP BY name
) b ON a.name = b.name AND
a.ReceiveTime = b.max_time
SET a.is_unread = 1
-- WHERE a.name = 'John'
没有 WHERE 条件.它将全部更新列 is_unread 以获取最新条目.
Without the WHERE condition. It will all update the column is_unread for the latest entry.
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