MySQL之-查詢/刪除重復記錄的方法大全詳解

查找所有重復標題的記錄:

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

一、查找重復記錄

1、查找全部重復記錄

Select?*?From?表?Where?重復字段?In?(Select?重復字段?From?表?Group?By?重復字段?Having?Count(*)>1)

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。
1、對于第一種重復,比較容易解決,使用

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

select?distinct?*?into?#Tmp?from?tableName  drop?table?tableName  select?*?into?tableName?from?#Tmp  drop?table?#Tmp

發生這種重復的原因是表設計不周產生的,增加唯一刪除列即可解決。
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
假設有重復的字段為Name,Address,要求得到這兩個字段唯一的結果集

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)

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