101高考 SQL - 高考

小弟SQL觀念薄弱
作了很多題目都覺得似是而非...有點慌
請問一下(二)作答是否正確?
是否有更有效率的作法?
(三)沒有頭緒...請問此小題該如何作答
謝謝
=======================101高考二級=============================
二、考慮以下的討論版資料庫綱目（Database schema）：
Member(mId, name, bDate, gender)
//會員編號，姓名，生日，性別
Article(mId, aId, title, content, postDate)
//會員編號，文章編號，標題，內容，張貼日期
Reply(mId, aId, rTime, content, responder)
//會員編號，文章編號，回覆日期時間，回覆內容，回覆者
若我們有以下的SQL敘述：

SELECT mId, name
FROM Member AS M
WHERE gender = ‘M’ AND
EXISTS
(SELECT *
FROM Article AS A
WHERE mId = M.mId AND (mId, aId) IN
(SELECT DISTINCT mId, aId
FROM Reply
WHERE mId = A.mId AND aId = A.aId
GROUP BY mId, aId
HAVING COUNT(*) > 10));
(二)以上查詢句的執行效率可能不佳，請指出造成其效率不佳的語法，並改寫成一個效率
較佳的敘述。（10分）
(三)針對你所改寫的查詢句，若想進一步提升其執行效率，請問可以建置那些索引（
Index）？請寫出建置這些索引的SQL敘述並說明原因。（10分）
============================================================================

擬作答:
(二)
SELECT mId, name
FROM Member AS M , Article AS A
WHERE gender = ‘M’ AND
A.mId = M.mId AND
(mId, aId) IN
(SELECT DISTINCT mId, aId
FROM Reply
WHERE mId = A.mId AND aId = A.aId
GROUP BY mId, aId
HAVING COUNT(*) > 10
)
);

--