按MAX（时间）选择最近的MySQL行时间＆lt; = x

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

查询不再有效。有没有子查询的解决方案吗？

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

或简单地说：

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

Answer 2

使用HAVING子句，如下所示：

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