Question

I have a table of preferences, called “txp_prefs”. I would like to return multiple preferences into a single row; the reason I prefer this to a simple concatenation is that I’m using a plugin in textpattern which can process the single row.

Here is the testing data I have:

------------------------------------------------
|Id | event   | name             |value        |
------------------------------------------------
| 1 | season  | season_start     | 12/10/2011  |
-----------------------------------------------
| 2 | season  | season_end       | 29/10/2011  |
------------------------------------------------
| 3 | season  | season_countdown | 7           |
------------------------------------------------
| 4 | another | test1            | result1     |
------------------------------------------------
| 3 |         | test2            | result2     |
------------------------------------------------

The final result I would like to get is:

----------------------------------------------------------
|event    | season_start | season_end | season_countdown |
----------------------------------------------------------
|season   | 12/10/2011   | 29/10/2011 | 7                |
----------------------------------------------------------

I can (obviously) create the separate queries to get each result independently; for example

SELECT t1.event, t1.val AS season_start FROM txp_prefs t1 WHERE t1.event="season" AND t1.name="season_start" (to get the season_start)
SELECT t2.event, t2.val AS season_end FROM txp_prefs t2 WHERE t2.event="season" AND t2.name="season_end" (to get the season_end)

But I get errors when I try to join the two together, eg like this:

SELECT t1.event, t1.val AS season_start FROM txp_prefs t1 WHERE t1.event="season" AND t1.name="season_start"
LEFT JOIN 
(SELECT t2.event, t2.val AS season_end FROM txp_prefs t2 WHERE t2.event="season" AND t2.name="season_end") t3
ON t1.event=t3.event

The error messages says it is something to do with the join (which I guessed anyway – the two individual queries work.

Any ideas? I have recently figured through joining different tables together, so I assume it is possible to join a table to itself.

Answer 1

Based on the structure given you can use

SELECT 
     MAX(CASE WHEN name = 'season_start' THEN value END) AS season_start,
     MAX(CASE WHEN name = 'season_end' THEN value END) AS season_end,
     MAX(CASE WHEN name = 'season_countdown' THEN value END) AS season_countdown
FROM txp_prefs
WHERE event='season'