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

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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