SQL學習_讓我知道自己懂得太少

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DELETE FROM     UC_GROUP_USER_TMP WHERE     ROWID IN (         SELECT             A . ROWID         FROM             UC_GROUP_USER_TMP A,             (                                 //獲取最小行號跟用戶名ID的數據，並group by user_id                 SELECT                     MIN (ROWID) AS browid,                     user_id                 FROM                     UC_GROUP_USER_TMP                 WHERE                     user_id IN (                                                 //記錄總數大於1的用戶信息                         SELECT                             user_id                         FROM                             (                                 SELECT                                     COUNT (*) num,                                     user_id                                 FROM                                     UC_GROUP_USER_TMP                                 GROUP BY                                     user_id //獲取所有user_id的記錄總數                             )                         WHERE                             num > 1                     )                 GROUP BY                     user_id             ) b         WHERE             A .user_id = b.user_id         AND A . ROWID > b.browid                 //A的用戶id = B.user_id 並且 A.行號大於B的行號     );             DELETE FROM     UC_ESTATE_USER_TMP WHERE     ROWID IN (         SELECT             A . ROWID         FROM             UC_ESTATE_USER_TMP A,             (         //獲取最小值的ID, user_id, company_code,TYPE號, 在進行group by user_id, company_code, "type"的值                 SELECT                     MIN (ROWID) AS browid,                     user_id,                     company_code,                     "TYPE"                 FROM                     UC_ESTATE_USER_TMP                 //能這麼where 哦 where(user_id, company_code, type) IN(select user_id, company_code, type from ***);         WHERE                     (                         user_id,                         company_code,                         "TYPE"                     ) IN (             //num值大於1的記錄例出來                         SELECT                             user_id,                             company_code,                             "TYPE"                         FROM                             (                 //將user_id, company_code, "TYPE"進行group三個值，user_id, company_code, TYPE的值                                 SELECT                                     COUNT (*) num,                                     user_id,                                     company_code,                                     "TYPE"                                 FROM                                     UC_ESTATE_USER_TMP                                 GROUP BY                                     user_id,                                     company_code,                                     "TYPE"                             )                         WHERE                             num > 1                     )                 GROUP BY                     user_id,                     company_code,                     "TYPE"             ) b         WHERE         A .user_id = b.user_id         AND A .company_code = b.company_code         AND A ."TYPE" = b."TYPE"         AND A . ROWID > b.browid //這個大於讓我不能理解 http://blog.ccguitar.cn/?uid-795123-action-viewspace-itemid-77460 http://blog.ccguitar.cn/?uid-795123-action-viewspace-itemid-77461 http://blog.ccguitar.cn/?uid-795123-action-viewspace-itemid-77462 http://blog.ccguitar.cn/?uid-795123-action-viewspace-itemid-77463 http://blog.ccguitar.cn/?uid-795123-action-viewspace-itemid-77464 http://blog.ccguitar.cn/index.php?uid-795123-action-viewspace-itemid-77458 http://blog.ccguitar.cn/index.php?uid-795123-action-viewspace-itemid-77457                 );