查询或删除表中相同的记录
比如现在有一人员表（表名：peosons） 若想将姓名、身份证号、住址这三个字段完全相同的记录查询出来   
select p1.* from persons p1,persons p2   
where p1.idp2.id and p1.cardid = p2.cardid and p1.pname = p2.pname and p1.address = p2.address 可以实现上述效果．   
几个删除重复记录的SQL语句   
1.用rowid方法   
2.用group by方法   
3.用distinct方法   
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:   
     select * from table1 a where rowid !=(select   max(rowid)   
     from table1 b where a.name1=b.name1 and a.name2=b.name2......)   
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:   
　　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   
删数据：   
　　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(*)