ORDER BY CASE Issue

Databases
1

OK, 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       |
-------------------------------------------------------------------

I need pull all 4 rows ORDER BY ‘timestamp_one’ if ‘id_one’=27 or ORDER BY ‘timestamp_two’ if ‘id_one’=27.

This is the statement I have now:

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

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       |
-------------------------------------------------------------------

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       |
-------------------------------------------------------------------

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.

2

Someone over at Stack Overflow came up with the answer. I wanted to post it in case anyone else wants to know.

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
3

would i be correct in concluding from your sample data that whenever id_one is 27, then timestamp_2 is NULL? and whenever id_two is 27, then timestamp_1 is NULL?

if so, you can simplify your query substantially

:slight_smile:

4

No, sometimes both ids are set and both timestamps are set. The query I am using is correct.