Question

我有一张桌子（table1）：

ID   INSERTDATE    ISSUE    SOURCE
1    2011-12-01    A        EMAIL
2    2011-12-02    B        POST
3    2011-12-03    C        MEETING
4    2011-12-04    B        INTERNET

我想为每个问题获取最新消息......

SELECT * FROM table1 GROUP BY SOURCE ORDER BY ISSUE ASC

结果

ID   INSERTDATE    ISSUE    SOURCE
1    2011-12-01    A        EMAIL
2    2011-12-02    B        POST
3    2011-12-03    C        MEETING

但是我怎样才能得到以下内容，以便问题B有最新的来源？

ID   INSERTDATE    ISSUE    SOURCE
1    2011-12-01    A        EMAIL
4    2011-12-04    B        INTERNET
3    2011-12-03    C        MEETING

Answer 1

您需要聚合和自我加入。
这是标准SQL，不依赖于扩展的MySQL组（are rubbish）

SELECT
    t.*
FROM
    ( -- get most recent ID per issue
    SELECT MAX(ID) AS MaxID, ISSUE
    FROM table1
    GROUP BY ISSUE
    ) t2
    JOIN  -- join back to get the whole row
    table1 t ON t2.MaxID = t.ID

评论后编辑。假设每天只更改一次

SELECT
    t.*
FROM
    ( -- get most recent INSERTDATE per issue
    SELECT MAX(INSERTDATE) AS MaxINSERTDATE, ISSUE
    FROM table1
    GROUP BY ISSUE
    ) t2
    JOIN  -- join back to get the whole row
    table1 t ON t2.MaxINSERTDATE = t.ID

Answer 2

我认为你应该通过INSERTDATE订购（也许，问题）

SELECT * FROM table1 GROUP BY SOURCE ORDER BY INSERTDATE DESC

MySQL - 使用GROUP BY的最新行

2 个答案: