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SELECT Count(UserId) usercount, yr, wk FROM (SELECT UserId, Year(CreationDate) yr, Datepart(wk, creationDate) wk FROM Comments UNION SELECT UserId, Year(CreationDate) yr, Datepart(wk, creationDate) wk FROM PostHistory UNION SELECT OwnerUserId, Year(CreationDate) yr, Datepart(wk, creationDate) wk FROM Posts) t GROUP BY yr, wk ORDER BY yr, wk