前言
本文主要給大家介紹了關于MySQL中查詢、刪除重復記錄的方法，分享出來供大家參考學習，下面來看看詳細的介紹：
查找所有重復標題的記錄：
| select title,count(*) as count from user_table group by title having count>1; |
| SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC |
一、查找重復記錄
1、查找全部重復記錄
| SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC |
2、過濾重復記錄(只顯示一條)
| Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title) |
注：此處顯示ID最大一條記錄
二、刪除重復記錄
1、刪除全部重復記錄（慎用）
| Delete 表 Where 重復字段 In (Select 重復字段 From 表 Group By 重復字段 Having Count(*)>1) |
2、保留一條（這個應該是大多數人所需要的 ^_^）
| Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title) |
注：此處保留ID最大一條記錄
三、舉例
1、查找表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷
| select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) |
2、刪除表中多余的重復記錄，重復記錄是根據單個字段（peopleId）來判斷，只留有rowid最小的記錄
| delete from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1) and rowid not in (select min(rowid) from people group by peopleId having count(peopleId )>1) |
3、查找表中多余的重復記錄（多個字段）
| select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) |
4、刪除表中多余的重復記錄（多個字段），只留有rowid最小的記錄
| delete from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1) |
5、查找表中多余的重復記錄（多個字段），不包含rowid最小的記錄
| select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1) and rowid not in (select min(rowid) from vitae group by peopleId,seq having count(*)>1) |
四、補充
有兩個以上的重復記錄，一是完全重復的記錄，也即所有字段均重復的記錄，二是部分關鍵字段重復的記錄，比如Name字段重復，而其他字段不一定重復或都重復可以忽略。
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