如何查出同一张表中字段值重复的记录,或者删除重复的记录

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Java
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:  删除重复的记录
  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  
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