一條SQL語句完美解決【去重留一】

本文轉載自：http://blog.diginfos.com/index.php?r=article/view&id=126

此處以某消費記錄表(consume_record)爲例，SQL語句以下：

DELETE consume_record
FROM
    consume_record, 
    (
        SELECT
            min(id) id,
            user_id,
            monetary,
            consume_time
        FROM
            consume_record
        GROUP BY
            user_id,
            monetary,
            consume_time
        HAVING
            count(*) > 1
    ) t2
WHERE
    consume_record.user_id = t2.user_id 
    and consume_record.monetary = t2.monetary
    and consume_record.consume_time  = t2.consume_time
AND consume_record.id > t2.id;

SQL語句分析：

一、查詢出重複記錄造成一個集合（臨時表t2），集合裏是每種重複記錄的最小ID

(SELECT min(id) id, user_id, monetary, consume_time FROM consume_record GROUP BY user_id, monetary, consume_time HAVING count(*) > 1 ) t2

二、關聯<判斷重複基準的字段

consume_record.user_id = t2.user_id and consume_record.monetary = t2.monetary and consume_record.consume_time = t2.consume_time

三、根據條件，刪除原表中id大於t2中id的記錄

DELETE consume_record FROM ... WHERE ... AND consume_record.id > t2.id;

測試效果：
圖一爲刪除前總記錄數45541，圖二爲刪除操做、從45541條記錄中刪除2800條重複記錄用時0.09秒，圖三爲刪除後總記錄數。貼上測試表，若有須要的小夥伴，下載導入便可進行測試。consume_record.sql

以下語句，用於SQL server對AccountEmail帳號信息去重：

DELETE [FSDBtemp].[dbo].[CusUsers]
FROM [FSDBtemp].[dbo].[CusUsers], 
    (
SELECT
            min(cuid) cuid,
            [AccountEmail]
        FROM
            [FSDBtemp].[dbo].[CusUsers]
        GROUP BY
                        [AccountEmail]
        HAVING
            count(*) > 1
    ) t2
WHERE
    [FSDBtemp].[dbo].[CusUsers].AccountEmail = t2.AccountEmail 
AND [FSDBtemp].[dbo].[CusUsers].cuid > t2.cuid