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mysql怎么查詢和刪除重復記錄

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文章目錄
  1. 查找重復記錄
  2. 刪除重復記錄
  3. 舉例
  4. 補充

查找所有重復標題的記錄:

  1. SELECT * FROM t_info a WHERE ((SELECT COUNT(*) FROM t_info WHERE Title = a.Title) > 1) ORDER BY Title DESC

查找重復記錄

查找全部重復記錄

  1. Select * FromWhere 重復字段 In (Select 重復字段 FromGroup By 重復字段 Having Count(*)>1)

過濾重復記錄(只顯示一條)

  1. 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

刪除重復記錄

刪除全部重復記錄(慎用)

  1. DeleteWhere 重復字段 In (Select 重復字段 FromGroup By 重復字段 Having Count(*)>1)

保留一條(這個應該是大多數人所需要的 ^_^)

  1. 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

舉例

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

  1. select * from people where peopleId in (select peopleId from people group by peopleId having count(peopleId) > 1)

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

  1. 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)

查找表中多余的重復記錄(多個字段)

  1. select * from vitae a where (a.peopleId,a.seq) in (select peopleId,seq from vitae group by peopleId,seq having count(*) > 1)

刪除表中多余的重復記錄(多個字段),只留有rowid最小的記錄

  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)

查找表中多余的重復記錄(多個字段),不包含rowid最小的記錄

  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)

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。

對于第一種重復,比較容易解決,使用

  1. select distinct * from tableName

就可以得到無重復記錄的結果集。

如果該表需要刪除重復的記錄(重復記錄保留1條),可以按以下方法刪除

  1. select distinct * into #Tmp from tableName
  2. drop table tableName
  3. select * into tableName from #Tmp
  4. drop table #Tmp

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。

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

假設有重復的字段為Name,Address,要求得到這兩個字段唯一的結果集

  1. select identity(int,1,1) as autoID, * into #Tmp from tableName
  2. select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,autoID
  3. select * from #Tmp where autoID in(select autoID from #tmp2)

原文:http://blog.csdn.net/l1028386804/article/details/51733585

來源:本文由思享SEO博客原創撰寫,歡迎分享本文,轉載請保留出處和鏈接!
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