MySQL获取组的最后一个元素

Question

Good morning,

I am trying to get the most up to date element of a group from the database but no luck so far. Ideas anyone? I guess the solution is quite easy but I am really stuck there...

Data:

+---------------+----------+-------+------------+---------------------+
| transition_id | field_id | value | changed_by | changed             |
+---------------+----------+-------+------------+---------------------+
| 3             | 1        | Data  | Mike       | 2018-08-13 00:00:00 |
| 3             | 2        | Data  | Mike       | 2018-08-13 00:00:00 |
| 3             | 3        | Data  | Mike       | 2018-08-13 00:00:00 |
| 3             | 1        | Data  | Mike       | 2018-08-20 00:00:00 |
| 4             | 1        | Data  | Mike       | 2018-08-15 00:00:00 |
+---------------+----------+-------+------------+---------------------+

Expected results:

+---------------+----------+-------+------------+---------------------+
| transition_id | field_id | value | changed_by | changed             |
+---------------+----------+-------+------------+---------------------+
| 3             | 2        | Data  | Mike       | 2018-08-13 00:00:00 |
| 3             | 3        | Data  | Mike       | 2018-08-13 00:00:00 |
| 3             | 1        | Data  | Mike       | 2018-08-20 00:00:00 |
| 4             | 1        | Data  | Mike       | 2018-08-15 00:00:00 |
+---------------+----------+-------+------------+---------------------+

Grouping: transition_id, field_id

I tried using a left join on the table itself, but this is only returning a single item.

SELECT t1.* 
FROM table t1 
LEFT JOIN table t2 ON (t1.event = t2.event AND t1.update < t2.update) 
WHERE t2.update IS NULL AND t1.event = 81 

Thank you for your help! André

Fiddle: http://sqlfiddle.com/#!9/b24ddb/4

Answer 1

Try this :

select x.* from tablename x
inner join 
(select event, item, max(update) as mupdate from tablename
group by event, item)a
on x.event=a.event and x.item=a.item and x.update=a.mupdate