MySQL之——查询重复记录、删除重复记录方法大全

以你之姓@ 2023-10-11 15:30 29阅读 0赞

查找所有重复标题的记录：

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

#### 一、查找重复记录 ####

1、查找全部重复记录

Select * From 表 Where 重复字段 In (Select 重复字段 From 表 Group By 重复字段 Having Count(*)>1)

2、过滤重复记录(只显示一条)

Select * From HZT Where ID In (Select Max(ID) From HZT Group By Title)

注：此处显示ID最大一条记录

#### 二、删除重复记录 ####

1、删除全部重复记录（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、保留一条（这个应该是大多数人所需要的 ^\_^） ####

Delete HZT Where ID Not In (Select Max(ID) From HZT Group By Title)

注：此处保留ID最大一条记录

#### 三、举例 ####

1、查找表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断

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

2、删除表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断，只留有rowid最小的记录

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、查找表中多余的重复记录（多个字段）

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

4、删除表中多余的重复记录（多个字段），只留有rowid最小的记录

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、查找表中多余的重复记录（多个字段），不包含rowid最小的记录

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、补充 ####

有两个以上的重复记录，一是完全重复的记录，也即所有字段均重复的记录，二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或都重复可以忽略。  
1、对于第一种重复，比较容易解决，使用

select distinct * from tableName

就可以得到无重复记录的结果集。  
如果该表需要删除重复的记录（重复记录保留1条），可以按以下方法删除

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

发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。  
2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下  
假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集

1.  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)