本文主要介紹了MySQL中查詢、刪除重複記錄的方法,分享出來供大家參考學習,以下來看看詳細的介紹。
尋找所有重複標題的記錄:
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、找出重複記錄
1、尋找全部重複記錄
SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
2、過濾重複記錄(只顯示一筆)
Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
註:此處顯示ID最大一筆記錄
二、刪除重複記錄
1、刪除全部重複記錄(慎用)
Delete 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 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)
#註:此處保留ID最大一筆記錄
#三、舉例
1、查找表中多餘的重複記錄,重複記錄是根據單一欄位(peopleId)來判斷
select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
2、刪除表中多餘的重複記錄,重複記錄是根據單一欄位(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、查找表中多餘的重複記錄(多個欄位)
select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
4、刪除表中多餘的重複記錄(多個欄位),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、查找表中多餘的重複記錄(多個欄位),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
有兩個以上的重複記錄,一是完全重複的記錄,也即所有欄位重複的記錄,二是部分關鍵欄位重複的記錄,例如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
就可以得到無重複記錄的結果集。
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
發生這種重複的原因是表設計不周產生的,增加唯一索引列即可解決。
2、這類重複問題通常要求保留重複記錄中的第一筆記錄,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)
總結
以上就是這篇文章的全部內容了,希望本文的內容對大家的學習或工作能帶來一定的幫助
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