Question

我尝试编写一个sql请求来查找每个组的最后一条记录，这是我的表的布局：

 --------------------------------------
| id | Group | message | Status | date|
 -------------------------------------
| 1  | A     | msg1    | sent   | dt  |
 -------------------------------------
| 2  | A     | msg2    |deferred| dt2 |
 -------------------------------------
| 3  | B     | msg3    |deferred| dt  |
 -------------------------------------
| 4  | B     | msg4    |deferred| dt  |
 -------------------------------------
| 5  | B     | msg5    |Bounced | dt  |
 -------------------------------------
| 6  | C     | msg6    |sent    | dt  |
 -------------------------------------
| 7  | D     | msg7    |deferred| dt  |
 -------------------------------------
| 8  | D     | msg8    |deferred| dt  |
 -------------------------------------
| 9  | D     | msg9    |sent    | dt  |
 -------------------------------------

我试着得到这个输出：

 --------------------------------------
| id | Group | message | Status | date|
 -------------------------------------
| 2  | A     | msg2    |deferred| dt  |
 -------------------------------------
| 5  | B     | msg5    |bounced | dt  |
 -------------------------------------
| 8  | D     | msg8    |deferred| dt  |
 -------------------------------------

这意味着我希望每个组使用我在表格中的日期最后一个“延期”或“退回”消息。我从做这个请求开始，但我不知道如何修改它以获得我想要的结果：

SELECT ee.Group, ee.message
FROM email_errors ee
LEFT JOIN email_errors ee2 ON ( ee.Group = ee2.Group
AND ee.id < ee2.id ) 
WHERE ee2.id IS NULL 
AND ee2.status <>0

我注意到ee.status＆lt;＆gt; 0因为在我的真实表中我替换了3个可能的状态bu 0,1,2，并且我将发送状态替换为0。

Answer 1

我会做以下事情：

SELECT ee.*
FROM email_errors as ee
CROSS JOIN
(
    SELECT ee.Group as grp, MAX(ee.id) AS max_id
    FROM email_errors as ee
    CROSS JOIN
    (
        SELECT Group as grp, MAX(date_t) AS max_date
          FROM email_errors
          WHERE status <> 0
          GROUP BY Group
    ) aux
    WHERE ee.Group = aux.grp
    AND ee.date_t = aux.max_date
    GROUP BY ee.Group
) outer_aux
WHERE ee.Group = outer_aux.grp
AND ee.id = outer_aux.max_id

Answer 2

请注意group是MySQL中的保留字 - 所以不是列的好名字......

SELECT x.* 
  FROM email_errors x 
  JOIN 
     ( SELECT email_group
            , MAX(id) max_id 
         FROM email_errors 
        WHERE status IN ('deferred','bounced') 
        GROUP 
           BY email_group
     ) y 
    ON y.email_group = x.email_group 
   AND y.max_id = x.id;

根据某些条件检索每个组的最后一条记录

2 个答案: