Three joins with aggregate functions issue

Question

I have three tables (MySQL):

matches:
 ___________________________
|match_static_id| team_name |
|_______________|___________|
|  1            |  Italy    |
|  2            |  France   |
|_______________|___________|

users:
 ___________________________
|user_id        | username  |
|_______________|___________|
|  1            |  Dolly    |
|  2            |  Didi     |
|_______________|___________|

forum:
 _____________________________________________________________
|match_static_id| comment   | timestamp            | user_id  |
|_______________|___________|______________________|__________|
|  1            |  Hi       | 2013-07-10 12:15:03  |     2    |
|  1            |  Hello    | 2013-07-09 12:14:44  |     1    | 
|_______________|___________|______________________|__________|

The following query is working fine (using just users,forum):

SELECT  f1.match_static_id,
  f2.comments_no, 
  f2.maxtimestamp, 
  users.username
FROM forum AS f1

INNER JOIN
(
  SELECT match_static_id, 
    max(timestamp) maxtimestamp,
    count(match_static_id) AS comments_no
  FROM forum
  GROUP BY match_static_id
) AS f2  ON f1.match_static_id = f2.match_static_id
        AND f1.timestamp = f2.maxtimestamp
INNER JOIN users on users.user_id = f1.user_id
Order BY f2.maxtimestamp DESC

But when I try to query some data from the third table also with this query:

SELECT  f1.match_static_id,
  f2.comments_no, 
  f2.maxtimestamp, 
  users.username,
  matches.team_name
FROM forum AS f1

INNER JOIN
(
  SELECT match_static_id, 
    max(timestamp) maxtimestamp,
    count(match_static_id) AS comments_no
  FROM forum
  GROUP BY match_static_id
) AS f2  ON f1.match_static_id = f2.match_static_id
        AND f1.timestamp = f2.maxtimestamp
INNER JOIN users on users.id = f1.user_id
INNER JOIN matches on matches.match_static_id = f2.match_static_id
Order BY f2.maxtimestamp DESC

The result was duplicated (each record is duplicated) I do not why I see everything is ok so if anybody have any idea that could help me please HELP!!!

Answer 1

You probably don't need to do the join on the inner select statement.

SELECT  
  f1.match_static_id,
  count(f1.comment) as comments_no, 
  max(timestamp) as maxtimestamp, 
  users.username,
  matches.team_name
FROM 
    forum AS f1
INNER JOIN users u on u.id = f1.user_id
INNER JOIN matches m on m.static_id = f1.match_static_id
GROUP BY m.match_static_id
ORDER BY maxtimestamp DESC

Answer 2

i think, You want to search for last Comment, so just use group by function

GROUP BY f1.match_static_id

SQL Fiddle - would be useful

and there is no "users.id" collumn