本文主要給大家介紹了關(guān)于mysql中查詢、刪除重復(fù)記錄的方法,分享出來供大家參考學(xué)習(xí),下面來看看詳細的介紹。
查找所有重復(fù)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、查找重復(fù)記錄
1、查找全部重復(fù)記錄
SELECT?*?FROM?t_info?a?WHERE?((SELECT?COUNT(*)?FROM?t_info?WHERE?Title?=?a.Title)?>?1)?ORDER?BY?Title?DESC
2、過濾重復(fù)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(fù)記錄
1、刪除全部重復(fù)記錄(慎用)
Delete?表?Where?重復(fù)字段?In?(Select?重復(fù)字段?From?表?Group?By?重復(fù)字段?Having?Count(*)>1)
2、保留一條(這個應(yīng)該是大多數(shù)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(fù)記錄,重復(fù)記錄是根據(jù)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(fù)記錄,重復(fù)記錄是根據(jù)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(fù)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(fù)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(fù)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(fù)記錄,一是完全重復(fù)的記錄,也即所有字段均重復(fù)的記錄,二是部分關(guān)鍵字段重復(fù)的記錄,比如Name字段重復(fù),而其他字段不一定重復(fù)或都重復(fù)可以忽略。
1、對于第一種重復(fù),比較容易解決,使用
select?distinct?*?from?tableName
就可以得到無重復(fù)記錄的結(jié)果集。
如果該表需要刪除重復(fù)的記錄(重復(fù)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(fā)生這種重復(fù)的原因是表設(shè)計不周產(chǎn)生的,增加唯一索引列即可解決。
2、這類重復(fù)問題通常要求保留重復(fù)記錄中的第一條記錄,操作方法如下
假設(shè)有重復(fù)的字段為Name,Address,要求得到這兩個字段唯一的結(jié)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(jié)