SQL查询重复记录操作

假设现有一张人员表（表名：Person），若想将姓名、身份证号、住址这三个字段完全相同的记录查找出来，使用

1:  SELECT p1.*   
   2:  FROM persons   p1,persons   p2   
   3:  WHERE p1.id<>p2.id   
   4:  AND p1.cardid   =   p2.cardid   
   5:  AND p1.pname   =   p2.pname   
   6:  AND p1.address   =   p2.address

可以实现该功能。

删除重复记录的SQL语句

1、用rowid方法

据据oracle带的rowid属性，进行判断，是否存在重复,语句如下： 

查数据: 

删数据： 

delete   from table1 a where rowid !=(select   max(rowid)    

      from table1 b where a.name1=b.name1 and a.name2=b.name2......)

2、group by方法

查数据: 

删数据： 

select count(num), max(name) from student --列出重复的记录数，并列出他的name属性  

 group by num  

 having count(num) >1 --按num分组后找出表中num列重复，即出现次数大于一次

delete from student  

 group by num  

 having count(num) >1

这样的话就把所有重复的都删除了。

3、用distinct方法 -对于小的表比较有用

create table table_new as   select distinct *   from table1 minux  

 truncate table table1;  

 insert into table1 select * from table_new;

查询及删除重复记录的方法大全 

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)

(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

＂重复记录＂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)