MYSQL ORDER BY CASE 问题

问题描述

我有一个这样的数据库:

I have a database like this:

-------------------------------------------------------------------
|   id_one   |   id_two   |   timestamp_one   |   timestamp_two   |
-------------------------------------------------------------------
|     27     |     35     |        9:30       |        NULL       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:35       |
-------------------------------------------------------------------
|     27     |     35     |        9:34       |        NULL       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:33       |
-------------------------------------------------------------------

我需要拉所有 4 行

ORDER BY 'timestamp_one' if 'id_one'=27 or 
ORDER BY 'timestamp_two' if 'id_one'=27

这是我现在的声明:

SELECT * FROM tablename 
WHERE id_one=27 OR id_two=27 
ORDER BY 
  CASE WHEN id_one=27 THEN timestamp_one END DESC, 
  CASE WHEN id_two=27 THEN timestamp_two END DESC

这很有效，因为输出如下:

This works good in that is outputs this:

-------------------------------------------------------------------
|   id_one   |   id_two   |   timestamp_one   |   timestamp_two   |
-------------------------------------------------------------------
|     27     |     35     |        9:30       |        NULL       |
-------------------------------------------------------------------
|     27     |     35     |        9:34       |        NULL       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:33       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:35       |
-------------------------------------------------------------------

但我需要两个时间戳列来排序，就像它们是一列一样，所以它会这样排序:

But I need to two timestamp columns to order like they are one so it would order like this:

-------------------------------------------------------------------
|   id_one   |   id_two   |   timestamp_one   |   timestamp_two   |
-------------------------------------------------------------------
|     27     |     35     |        9:30       |        NULL       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:33       |
-------------------------------------------------------------------
|     27     |     35     |        9:34       |        NULL       |
-------------------------------------------------------------------
|     35     |     27     |        NULL       |        9:35       |
-------------------------------------------------------------------

我希望这是有道理的.本质上，我试图有两个特定于 WHERE 条件的 ORDER BY 列.然后，一旦为该行选择了正确的 ORDER BY 列，它就会按整个时间戳对 ROWS 进行排序.

I hope this makes sense. Essentially, I am trying to have two ORDER BY columns that are specific to a WHERE condition. Then once the correct ORDER BY column is chosen for that row, it orders the ROWS by the timestamp as a whole.

推荐答案

SELECT id_one, id_two, timestamp_one, timestamp_two      
FROM tablename 
WHERE id_one = 27 
    OR id_two = 27 
ORDER BY 
    CASE 
        WHEN id_one=27 THEN timestamp_one 
        WHEN id_two=27 THEN timestamp_two 
    END DESC 

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