SQLで集計

3つのテーブルで子テーブルの数を数えたい場合のSQLうまくいきました

テーブル
A{ aid }
B{ bid, aid }
C{ cid, aid }

SELECT A.aid,COUNT(B.bid),COUNT(C.cid) FORM
 A LEFT JOIN B ON A.aid = B.aid LEFT JOIN C ON A.aid = C.aid GROUP BY A.aid

DISTINCTがCOUNT関数にいるのですね...

SELECT A.aid,COUNT(DISTINCT B.bid),COUNT(DISTINCT C.cid) FORM
 A LEFT JOIN B ON A.aid = B.aid LEFT JOIN C ON A.aid = C.aid GROUP BY A.aid