oracle去除重复数据的⽅法
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
代码如下:
select p1.*
from persons  p1,persons  p2
where p1.id<>p2.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:
代码如下:
select * from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=)
删数据：
代码如下:
delete  from table1 a where rowid !=(select max(rowid)
from table1 b where a.name1=b.name1 and a.name2=)
查数据:
代码如下:
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分组后出表中num列重复，即出现次数⼤于⼀次
删数据：
代码如下:
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
代码如下:
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、查表中多余的重复记录，重复记录是根据单个字段（peopleId）来判断
代码如下:
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
代码如下:
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、查表中多余的重复记录（多个字段）
代码如下
select * from vitae a
select中distinct
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
代码如下:
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、查表中多余的重复记录（多个字段），不包含rowid最⼩的记录
代码如下:
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；
代码如下:
Select Name,Count(*) From A Group By Name Having Count(*) > 1
如果还查性别也相同⼤则如下:
代码如下:
Select Name,sex,Count(*) From A Group By Name,sex Having Count(*) > 1
(三)
⽅法⼀
代码如下:
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
代码如下:
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
代码如下:
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
代码如下:
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
代码如下:
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1
)