由MAX（時間），時間選擇最近的MySQL行<= X

Question

我選擇最近的一個MySQL表的項目有：

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

我的問題是，如果我想限制的最大時間與：

WHERE time <= nnn 

該查詢不起作用了。有沒有子查詢的解決方案？

在此先感謝！

Answer 1

使用HAVING子句，像這樣：

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

Answer 2

你可以用子查詢做到這一點：

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

或者乾脆：

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