SQL query doesn't work when using UNION?

Question

Here is the snapshot of the query that doesn't work since I added the Union.

SELECT fin05_usager.idUsager,
       (SELECT sum(nombreReputation) as nombreReputation
          FROM (SELECT SUM(nombreReputationGagner) as nombreReputation
                 FROM fin05_usager_reputation 
                WHERE fin05_usager_reputation.idUsager = fin05_usager.idUsager
             GROUP BY fin05_usager_reputation.idUsager
        UNION
                SELECT SUM(cc_badge.valeurEnReputation) as nombreReputation
                  FROM cc_badge, fin05_usager_badge
                 WHERE fin05_usager_badge.idBadge = cc_badge.idBadge
                   AND fin05_usager_badge.idUsager = fin05_usager.idUsager) as repuUnion    
       ) as repu
 FROM fin05_usager
WHERE fin05_usager.idUsager = 6

The error is : #1054 - Unknown column 'fin05_usager.idUsager' in 'where clause'

If I remove the fin05_usager.idUsager and use directly '6' it does work.

If I remove the union and use only one of the 2 select it works (what ever if I take the FROM fin05_usager_reputation or the other one FROM cc_badge, fin05_usager_badge.

Why when using the UNION the error about finding the idUsager appear and without the union no error is found?

Schema simplified:

fin05_usager: idUsager int(8)

fin05_usager_reputation : idUsager int(8), nombreReputationGagner int(4)

cc_badge : idBadge int(4), valeurEnReputation int(4)

fin05_usager_badge : idUsager int(8), idBadge int(4)

Note:

I cannot do the subquery directly in the query. I have to use it inside a subquery in the select because in real, the query is very big and already contain Group, etc.

Answer 1

Alright,

The only way I found for the moment without doing a Group By in the main query (since in the real situation I can't because it does contain already a Group By clause) is to do it in 2 and to merge it with the code... not exaclty what I would like but it works at least:

    SELECT fin05_usager.idUsager,

                (SELECT sum(nombreReputationGagner) as nombreReputation1
                FROM fin05_usager_reputation 
                WHERE fin05_usager_reputation.idUsager = fin05_usager.idUsager
                group by fin05_usager_reputation.idUsager) as nombreReputation1
            ,
                (SELECT sum(cc_badge.valeurEnReputation) as nombreReputation2
                FROM cc_badge,  fin05_usager_badge
                WHERE fin05_usager_badge.idBadge = cc_badge.idBadge
                AND fin05_usager_badge.idUsager = fin05_usager.idUsager) as nombreReputation2

    FROM 
        fin05_usager
        where fin05_usager.idUsager = 6

In the code I sum the nombreReputation1 and nombreReputation2.