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.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:
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(*) >； 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
)
