Requête MySQL Union dupliquée/groupée par problème

Tout n'est pas une union -- dans ce cas, il s'agit d'une jointure sur les sous-requêtes :

SELECT shpUserAdded AS userName, merCount, prdCount
FROM (SELECT shpUserAdded, count(*) AS shpCount FROM shops GROUP BY shpUserAdded ASC) AS s
JOIN (SELECT prdUserAdded, count(*) AS prdCount FROM products GROUP BY prdUserAdded ASC) AS p
ON (shpUserAdded = prdUserAdded);