mysql - 按 MAX(time) WHERE time <= x 选择最近的 MySQL 行

Question

我正在选择 MySQL 表的最新条目：

SELECT MAX(time) as most_recent, userID
FROM TableName
GROUP BY userID
ORDER BY most_recent DESC

我的问题是，如果我想限制最长时间：

WHERE time <= nnn

查询不再起作用。有没有子查询的解决方案？

提前致谢！

Answer 1

你可以用子查询来做到这一点：

select t.userID, max(t.time)
from
   (
     select userID, time
     from tableName
     where time <= nnn
   ) t
group by t.userID

或者简单地说：

     select userID, max(time)
     from tableName
     where time <= nnn
     group by userID

Answer 2

像这样使用HAVING子句：

SELECT MAX(time) as most_recent, userID
FROM TableName
GROUP BY userID
HAVING MAX(time) <= nnn
ORDER BY most_recent DESC