MySQL: Problem with max() and group by - wrong values

Question

Hello to all!

I have a problem with a SQL statement: Using this

select a.id as ID, a.dur as DUR, DATE(FROM_UNIXTIME(timestampCol)) as date, 
 a_au.re as RE, a_au.stat as STAT from b_c
  inner join c on b_c.c_id = c.id
  inner join a on c.id = a.c_id
  inner join a_au on a.id = a_au.id
  inner join revi on a_au.rev = revi.rev
  where b_c.b_id = 5

I get this result:

ID  DUR         date   RE  STAT
-------------------------------
31, 10, '2010-07-14', 2200, 0
31, 10, '2010-07-14', 2205, 0
31, 10, '2010-07-14', 2206, 2
31, 10, '2010-07-14', 2207, 0
31, 10, '2010-07-14', 2210, 2
31, 10, '2010-07-15', 2211, 0
31, 10, '2010-07-14', 2213, 1
32, 10, '2010-07-14', 2203, 0
32, 10, '2010-07-14', 2204, 0
32, 10, '2010-07-14', 2208, 2
32, 10, '2010-07-14', 2209, 0
32, 10, '2010-07-15', 2212, 2

Now I want to get one result row for one ID and date combination. Also I want to get this result row with the highest RE number.

So I write my statement:

select a.id as ID, a.dur as DUR, DATE(FROM_UNIXTIME(timestampCol)) as date, 
 max(a_au.re) as RE, a_au.stat as STAT from b_c
  inner join c on b_c.c_id = c.id
  inner join a on c.id = a.c_id
  inner join a_au on a.id = a_au.id
  inner join revi on a_au.rev = revi.rev
  where b_c.b_id = 5
  group by ID, date

Now I get this result:

ID  DUR         date   RE  STAT
-------------------------------
31, 10, '2010-07-14', 2213, 0
31, 10, '2010-07-15', 2211, 0
32, 10, '2010-07-14', 2209, 0
32, 10, '2010-07-15', 2212, 2

Everything seems to be okay, I have one result row per day/ID combination and the row with the highest RE number. But: the column STAT does not have the correct values! The row

31, 10, '2010-07-14', 2213, 0

must have the status 1:

31, 10, '2010-07-14', 2213, 1

So there must be a mistake in my statement. It seems that MySQL takes the first STAT column value it found. But I want to have the corresponding one.

What should I do? I saw other topics about this like here: http://stackoverflow.com/questions/1305056/mysql-selecting-all-corresponding-fields-using-max-and-group-by but I can not transfer it to my SQL statement.

Thanks a lot in advance & Best Regards.

Answer 1

Use:

SELECT a.id as ID, 
       a.dur as DUR, 
       DATE(FROM_UNIXTIME(timestampCol)) as date, 
       a_au.re as RE, 
       a_au.stat as STAT 
 FROM b_c
 JOIN c on b_c.c_id = c.id
 JOIN a on c.id = a.c_id
 JOIN a_au on a.id = a_au.id
 JOIN revi on a_au.rev = revi.rev
 JOIN ( SELECT a.id as ID, 
               DATE(FROM_UNIXTIME(timestampCol)) as date, 
               MAX(a_au.re) as Max_RE
          FROM b_c
          JOIN c on b_c.c_id = c.id
          JOIN a on c.id = a.c_id
          JOIN a_au on a.id = a_au.id
          JOIN revi on a_au.rev = revi.rev
         WHERE b_c.b_id = 5 
      GROUP BY a.id, DATE(FROM_UNIXTIME(timestampCol))) x ON x.id = a.id
                                                         AND x.date = DATE(FROM_UNIXTIME(timestampCol))
                                                         AND x.max_re = a_au.re
WHERE b_c.b_id = 5 

Sadly, MySQL doesn't support the WITH clause which could've made this a lot easier to read.