SQL根据计算列的最小值获取整个行 [英] SQL Get entire row based on minimum value of calculated column
问题描述
我有一张表格，其中有多个具有不同状态的床位ID值，诸如此类.
I have a table with multiple values of bed ID with different statuses, something like this.
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
我希望查询根据状态值为每个bed_id获取单个行.
我已经尝试过:
I want a query to get a single row for each bed_id based on the value of status.
I've tried:
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
但这给了我
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值正确，但其余行与StatusOrder值最小的行不对应)
(The StatusOrder value is right, but the rest of the row does not correspond to the row with minimum StatusOrder value)
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
我已阅读 MySQL MIN/MAX全部行 并尝试了这个:
I've read MySQL MIN/MAX all row and also tried this:
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)
But this produces an error. (Also tried replacing StatusOrder with the full CASE statement)
注意:我已经简化了包含更多列的实际表.但是基本上，我需要访问与每个bed_id具有最低StatusOrder(由我的case语句确定)的行相对应的整行.
NOTE: I've simplified the actual table which has many more columns. But basically I need access to the whole row that corresponds to the row with the lowest StatusOrder (determined by my case statement) for each bed_id.
使用MySQL 5.5
Using MySQL 5.5
推荐答案
以下查询有效，但最好考虑使用代码用status_code替换列状态，并使用单独的表status(status_code,description) {denormalise}
The Below Query works, but it's better to consider replace the column status with status_code with the code, and have a separate table status(status_code,description) {denormalise}
并索引(term_id,statUs_code).
由此，我们可以自我加入.而是创建这样的视图.
by this, we can just self join. Instead creating a view like this.
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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