MySQL之——查詢重複記錄、刪除重複記錄方法大全
阿新 • • 發佈:2019-02-13
查詢所有重複標題的記錄:
- SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
一、查詢重複記錄
1、查詢全部重複記錄
- Select * From 表 Where 重複欄位 In (Select 重複欄位 From 表 Group By 重複欄位 Having Count(*)>1)
2、過濾重複記錄(只顯示一條)
- Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
二、刪除重複記錄
1、刪除全部重複記錄(慎用)
- Delete 表 Where 重複欄位 In (Select 重複欄位 From 表 Group By 重複欄位 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)
三、舉例
1、查詢表中多餘的重複記錄,重複記錄是根據單個欄位(peopleId)來判斷
- select * from people where
- 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
- select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
- 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)
- 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
有兩個以上的重複記錄,一是完全重複的記錄,也即所有欄位均重複的記錄,二是部分關鍵欄位重複的記錄,比如Name欄位重複,而其他欄位不一定重複或都重複可以忽略。
1、對於第一種重複,比較容易解決,使用
- select distinct * from tableName
如果該表需要刪除重複的記錄(重複記錄保留1條),可以按以下方法刪除
- select distinct * into #Tmp from tableName
- drop table tableName
- select * into tableName from #Tmp
- drop table #Tmp
2、這類重複問題通常要求保留重複記錄中的第一條記錄,操作方法如下
假設有重複的欄位為Name,Address,要求得到這兩個欄位唯一的結果集
- select identity(int,1,1) as autoID, * into #Tmp from tableName
- select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
- select * from #Tmp where autoID in(select autoID from #tmp2)