SQL重复记录查询 查询多个字段、多表查询、删除重复记录的方法_Mysql

SQL重复记录查询

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)

例二： 

select * from testtable
where numeber in (select number from people group by number having count(number) > 1 )

可以查出testtable表中number相同的记录  

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)

(二) 

比方说 

在A表中存在一个字段“name”， 

而且不同记录之间的“name”值有可能会相同， 

现在就是需要查询出在该表中的各记录之间，“name”值存在重复的项； 

Select Name,Count(*) From A Group By Name Having Count(*) > 1

如果还查性别也相同大则如下： 

Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1

(三) 

方法一 

declare @max integer,@id integer 

declare cur_rows cursor local for select 主字段,count(*) from 表名 group by 主字段 having count(*) >； 1 

open cur_rows 

fetch cur_rows into @id,@max 

while @@fetch_status=0 

begin 

select @max = @max -1 

set rowcount @max 

delete from 表名 where 主字段 = @id 

fetch cur_rows into @id,@max 

end 

close cur_rows 

set rowcount 0 

方法二  

有两个意义上的重复记录，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 

select distinct * into #Tmp from tableName 

drop table tableName 

select * into tableName from #Tmp 

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 

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)

最后一个select即得到了Name，Address不重复的结果集（但多了一个autoID字段，实际写时可以写在select子句中省去此列）  

(四)  

查询重复 

select * from tablename where id in ( 

select id from tablename  

group by id  

having count(id) > 1 

) 

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