MySQL的 - 如何獲得使用GROUP最後一個記錄BY

Question

我有一個表像下面：

id | deptid | last_activities 
1 |  1  | MMD PURCASHING 
2 |  1  | JKO/REPORTING 
3 |  2  | STAND BY CC 
4 |  3  | JKO/REPORTING 

我的查詢：

SELECT id, deptid, last_activities FROM dept_activities GROUP BY deptid ORDER BY id DESC 

而結果如下圖所示：

id | deptid | last_activities 
4 |  3  | JKO/REPORTING 
3 |  2  | STAND BY CC 
1 |  1  | MMD PURCASHING 

在那裏我想要這樣的結果：

id | deptid | last_activities 
4 |  3  | JKO/REPORTING 
3 |  2  | STAND BY CC 
2 |  1  | JKO/REPORTING 

這怎麼可能？如何正確查詢？

Answer 1

請試試這個：

SELECT * FROM dept_activities AS da1 
JOIN 
(SELECT MAX(id) as max_id FROM dept_activities GROUP BY deptid DESC) AS da2 
ON (da1.id = da2.max_id); 

Answer 2

使用子查詢來獲取每個DEPTID最大ID，然後加入，對錶爲您提供了這樣的事情： -

SELECT a.id, a.deptid, a.last_activities 
FROM dept_activities a 
INNER JOIN 
(
    SELECT MAX(id) AS MaxId, deptid 
    FROM dept_activities 
    GROUP BY deptid 
) Sub1 
ON a.deptid = Sub1.deptid 
AND a.id = Sub1.MaxId 
ORDER BY a.id DESC 

另一個可能的解決方案使用GROUP_CONCAT，儘管對此並不熱衷（如果last_activity包含您用於GROUP_CONCAT的分隔符，則會失敗）。

SELECT MAX(id), deptid, SUBSTRING_INDEX(GROUP_CONCAT(last_activities ORDER BY id DESC), ',', 1) 
FROM dept_activities 
GROUP BY a.deptid