前言
本文主要給大家介紹了關于MySQL中查詢、洗掉重復記錄的方法，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：
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select title,count(*) as count from user_table group by title having count>1;
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SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
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一、查找重復記錄
1、查找全部重復記錄
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SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC
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2、過濾重復記錄(只顯示一條)
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Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)
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注：此處顯示ID最大一條記錄
二、洗掉重復記錄
1、洗掉全部重復記錄（慎用）
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Delete 表 Where 重復欄位 In (Select 重復欄位 From 表 Group By 重復欄位 Having Count(*)>1)
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2、保留一條（這個應該是大多數人所需要的 ^_^）
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Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)
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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欄位（peopleId）來判斷
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select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)
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2、洗掉表中多余的重復記錄，重復記錄是根據單個欄位（peopleId）來判斷，只留有rowid最小的記錄
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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)
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3、查找表中多余的重復記錄（多個欄位）
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select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)
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4、洗掉表中多余的重復記錄（多個欄位），只留有rowid最小的記錄
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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)
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5、查找表中多余的重復記錄（多個欄位），不包含rowid最小的記錄
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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)
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四、補充
有兩個以上的重復記錄，一是完全重復的記錄，也即所有欄位均重復的記錄，二是部分關鍵欄位重復的記錄，比如Name欄位重復，而其他欄位不一定重復或都重復可以忽略，
1、對于第一種重復，比較容易解決，使用
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select distinct * from tableName
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就可以得到無重復記錄的結果集，
如果該表需要洗掉重復的記錄（重復記錄保留1條），可以按以下方法洗掉
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select distinct * into #Tmp from tableName
drop table tableName
select * into tableName from #Tmp
drop table #Tmp
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發生這種重復的原因是表設計不周產生的，增加唯一索引列即可解決，
2、這類重復問題通常要求保留重復記錄中的第一條記錄，操作方法如下
假設有重復的欄位為Name,Address，要求得到這兩個欄位唯一的結果集
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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)
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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者作業能帶來一定的幫助
原文鏈接：http://blog.phpsoho.com/2017/06/20/mysql之-查詢重復記錄、洗掉重復記錄方法大全/
轉載請註明出處，本文鏈接：https://www.uj5u.com/shujuku/107764.html
標籤：MySQL