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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