从具有最新条目的另一个表中选择值

Question

I have 2 MySQL Tables:

Table with all Events

+----+---------------------+
| id | Eventtitle          |
+----+---------------------+
|  1 | Event 1             |
|  2 | Event 2             |
|  3 | Event 3             |
|  4 | Event 4             |
+----+---------------------+

Table with user attend statuses - Users can change their status multiple times. Every time they change it, a new entry is inserted into the table

+----+------------+----------+---------+---------------------+
| id | event_id   | user_id  | status  | attend_time         |
+----+------------+----------+---------+---------------------+
|  1 | 1          | 2        | 1       |2013-07-03 15:34:02  |
|  2 | 1          | 2        | 2       |2013-08-03 19:01:02  |  <--
|  3 | 3          | 1        | 1       |2013-07-03 15:34:02  |
|  4 | 4          | 4        | 3       |2013-07-03 15:34:02  |
|  5 | 4          | 6        | 2       |2013-07-03 15:34:02  |
|  6 | 4          | 6        | 1       |2013-07-03 18:55:02  |  <--
+----+-----------------------+---------+---------------------+

Now I want all events listed and additionally the most recent attend state and attend_time of the currently logged in user (for example user_id 2 oder 54) - IF he is not in the attend table i still need an entry of the event. (in that case a NULL for the state and attend_time would be good)

Here I rebuild the Data Structure: http://sqlfiddle.com/#!2/c1b3f

IF there is no way on how to get the result with MySQL - I will try to get it with PHP

Answer 1

Try something like this:

SELECT s.id, eventtitle, status, attend_time
FROM events e
JOIN status s ON e.id = s.event_id
WHERE user_id = 2 AND attend_time = (SELECT MAX(attend_time) FROM status
                                       WHERE user_id = 2)

SQLFiddle

Or:

SELECT s.id, eventtitle, s.status, s.attend_time
FROM events e
JOIN status s ON e.id = s.event_id
LEFT JOIN status s2 ON s.attend_time < s2.attend_time
WHERE s.user_id = 2 AND  s2.attend_time IS NULL

SQLFiddle

Answer 2

（未测试）

SELECT a.id, eventtitle, status, attend_time FROM events b JOIN status a ON b.id = a.event_id WHERE user_id = 2 order by attend_time desc