MySQL wrong results with GROUP BY and ORDER BY

Question

I have a table user_comission_configuration_history and I need to select the
last Comissions configuration from a user_id.

Tuples:

I’m trying with many queries, but, the results are wrong. My last SQL:

SELECT *
    FROM(
        SELECT * FROM user_comission_configuration_history
        ORDER BY on_date DESC
    ) AS ordered_history
WHERE user_id = 408002
GROUP BY comission_id

The result of above query is:

But, the correct result is:

id    user_id    comission_id    value         type          on_date
24    408002     12              0,01          PERCENTUAL    2014-07-23 10:45:42
23    408002     4               0,03          CURRENCY      2014-07-23 10:45:41
21    408002     6               0,015         PERCENTUAL    2014-07-23 10:45:18

What is wrong in my SQL?

Answer 1

This is your query:

SELECT *
FROM (SELECT *
      FROM user_comission_configuration_history
      ORDER BY on_date DESC
     ) AS ordered_history
WHERE user_id = 408002
GROUP BY comission_id;

One major problem with your query is that it uses a MySQL extension to group by that MySQL explicitly warns against. The extension is the use of other
columns in the in theselect that are not in the group by or in aggregation
functions. The warning (here) is:

MySQL extends the use of GROUP BY so that the select list can refer to
nonaggregated columns not named in the GROUP BY clause. This means that the
preceding query is legal in MySQL. You can use this feature to get better
performance by avoiding unnecessary column sorting and grouping. However,
this is useful primarily when all values in each nonaggregated column not
named in the GROUP BY are the same for each group. The server is free to
choose any value from each group, so unless they are the same, the values
chosen are indeterminate.

So, the values returned in the columns are indeterminate.

Here is a pretty efficient way to get what you want (with “comission” spelled
correctly in English):

SELECT *
FROM user_commission_configuration_history cch
WHERE NOT EXISTS (select 1
                  from user_commission_configuration_history cch2
                  where cch2.user_id = cch.user_id and
                        cch2.commission_id = cch.commission_id and
                        cch2.on_date > cch.on_date
                 ) AND
      cch.user_id = 408002;