mysql - 子查询获取最后一条记录

Question

我有 2 张桌子：User和Session. 对于每个用户，我想知道会话表中的最后一条记录是否是去年创建的。

我尝试了以下方法，但它不起作用：

SELECT *
FROM(
    SELECT MAX(`Session`.acDateF) as MaxDateF
    FROM `Session`
    WHERE `Session`.acType='1'
) as AcDate
GROUP BY `Session`.userId) 
WHERE YEAR(`Session`.acDateF) =YEAR(CURRENT_DATE())-1

如果用户今年在表中有记录，则Session它不会出现在结果中。

Answer 1

你的问题不是很清楚，但听起来你想要这样的东西：

SELECT * 
FROM `Session` s
INNER JOIN 
(
    SELECT MAX(`Session`.acDateF) as MaxDateF, `Session`.userId
    FROM `Session`
    WHERE `Session`.acType='1'
        AND YEAR(s.acDateF) =YEAR(CURRENT_DATE())-1
    GROUP `Session`.userId
) as AcDate
    ON s.userId = AcDate.userId
    AND s.acDateF = AcDate.MaxDateF;

或者，如果您想要用户数据：

SELECT * 
FROM `user` u
INNER JOIN 
(
    SELECT MAX(`Session`.acDateF) as MaxDateF, `Session`.userId
    FROM `Session`
    WHERE `Session`.acType='1'
        AND YEAR(s.acDateF) =YEAR(CURRENT_DATE())-1
    GROUP `Session`.userId
) as AcDate
    ON u.userId = AcDate.userId;    

Answer 2

SELECT
    MAX(`Session`.acDateF) as MaxDateF,
    `Session`.userId
FROM `Session`
WHERE `Session`.acType='1'
GROUP BY `Session`.userId
having MAX(YEAR(`Session`.acDateF)) as MaxDateF =YEAR(CURRENT_DATE())-1

Answer 3

这是一种方法。它使用子句中的相关子查询where来获取上一年的最后日期：

select *
from session s
where s.acDatef = (select MAX(se.acDatef)
                   from session s2
                   where s2.userid = s.userid and
                         YEAR(`Session`.acDateF) =YEAR(CURRENT_DATE())-1
                  )