/MySQL: Gemeinsamkeiten von Usern finden

[AllesMeins]

  
SELECT *  
FROM  
   (SELECT userId, artistId  
    FROM userTitel LEFT JOIN titel  
    USING (titelId)  
    GROUP BY artistId, userId) as t1  
JOIN  
   (SELECT userId, artistId  
    FROM userTitel LEFT JOIN titel  
    USING (titelId)  
    GROUP BY artistId, userId) as t2  
ON t1.artistId = t2.artistId