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mysql – SQL根据计算列的最小值获取整行

发布时间:2019-04-12 发布网站:脚本之家
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我有一张桌子,床身ID有多个不同的状态,就像这样.

PID     |  term_id   |  student_id   |  bed_id   | status    |  Comment
--------+------------+---------------+-----------+-----------+----------------
1       |  29        |  1234         |  751      | Canceled  |  Not this one
2       |  29        |  1234         |  751      | Active    |  This one
3       |  29        |  531          |  752      | Active    |  This one too
4       |  29        |  823          |  752      | Canceled  |  Not this one either
5       |  29        |  525          |  753      | Canceled  |  But this one too

我想要一个查询,根据状态值为每个bed_id获取一行.
我试过了:

SELECT *,MIN(CASE sample.status
                         WHEN 'Arrived' THEN 1
                         WHEN 'Active' THEN 2
                         WHEN 'Pending Approval' THEN 3
                         WHEN 'Pending Confirmation' THEN 4
                         WHEN 'Pending Manual' THEN 5
                         WHEN 'Denied' THEN 6
                         WHEN 'Canceled' THEN 7
                END) AS StatusOrder
FROM sample
WHERE (sample.term_id = 29)
GROUP BY bed_id

但它给了我:

PID  |  term_id |  student_id |  bed_id | status    |  Comment           | StatusOrder
------------------------------------------------------------------------------------
1    |  29      |  1234       |  751    | Canceled  |  Not this one      | 2
3    |  29      |  531        |  752    | Active    |  This one too      | 2
5    |  29      |  525        |  753    | Canceled  |  But this one too  | 7

(StatusOrder值是正确的,但行的其余部分与具有最小StatusOrder值的行不对应)

我想要的是:

PID  |  term_id |  student_id |  bed_id | status    |  Comment           | StatusOrder
------------------------------------------------------------------------------------
2    |  29      |  1234       |  751    | Active    |  This one          | 2
3    |  29      |  531        |  752    | Active    |  This one too      | 2
5    |  29      |  525        |  753    | Canceled  |  But this one too  | 7

我读过MySQL MIN/MAX all row
并试过这个:

SELECT *,MIN(CASE sample.status
                         WHEN 'Arrived' THEN 1
                         WHEN 'Active' THEN 2
                         WHEN 'Pending Approval' THEN 3
                         WHEN 'Pending Confirmation' THEN 4
                         WHEN 'Pending Manual' THEN 5
                         WHEN 'Denied' THEN 6
                         WHEN 'Canceled' THEN 7
                END) AS StatusOrder
FROM  sample
WHERE ( 
        (sample.term_id = 29) AND (
        StatusOrder = CASE sample.status
                         WHEN 'Arrived' THEN 1
                         WHEN 'Active' THEN 2
                         WHEN 'Pending Approval' THEN 3
                         WHEN 'Pending Confirmation' THEN 4
                         WHEN 'Pending Manual' THEN 5
                         WHEN 'Denied' THEN 6
                         WHEN 'Canceled' THEN 7
                END)
       )
GROUP BY bed_id

但这会产生错误. (还尝试用完整的CASE语句替换StatusOrder)

注意:我已经简化了具有更多列的实际表.但基本上我需要访问每个bed_id对应于具有最低StatusOrder(由我的case语句确定)的行的整行.

使用MySQL 5.5

最佳答案
下面的查询工作正常,但最好考虑用status_code替换列状态和代码,并具有单独的表状态(status_code,description){denormalise}

和索引(term_id,statUs_code).

通过这个,我们可以自己加入.而是创建这样的视图.

SELECT * FROM
(SELECT *,(CASE sample.status
                         WHEN 'Arrived' THEN 1
                         WHEN 'Active' THEN 2
                         WHEN 'Pending Approval' THEN 3
                         WHEN 'Pending Confirmation' THEN 4
                         WHEN 'Pending Manual' THEN 5
                         WHEN 'Denied' THEN 6
                         WHEN 'Canceled' THEN 7
                END) AS status_code FROM SAMPLE
  WHERE sample.term_id = 29
) my_view1,(SELECT BED_ID,MIN(CASE sample.status
                         WHEN 'Arrived' THEN 1
                         WHEN 'Active' THEN 2
                         WHEN 'Pending Approval' THEN 3
                         WHEN 'Pending Confirmation' THEN 4
                         WHEN 'Pending Manual' THEN 5
                         WHEN 'Denied' THEN 6
                         WHEN 'Canceled' THEN 7
                END) AS status_code FROM SAMPLE
 WHERE sample.term_id = 29
 GROUP BY BED_ID
) my_view2
WHERE my_view1.bed_id = my_view2.bed_id
 AND  my_view1.status_code = my_view2.status_code

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