例如：
id?????????? name???????? value
1?????????????? a???????????????? pp
2?????????????? a???????????????? pp
3?????????????? b???????????????? iii
4?????????????? b???????????????? pp
5?????????????? b???????????????? pp
6?????????????? c???????????????? pp
7?????????????? c???????????????? pp
8?????????????? c???????????????? iii
id是主键
要求得到这样的结果
id?????????? name???????? value
1?????????????? a???????????????? pp
3?????????????? b???????????????? iii
4?????????????? b???????????????? pp
6?????????????? c???????????????? pp
8?????????????? c???????????????? iii
方法1
delete?? YourTable??
where?? [id]?? not?? in?? (
select?? max([id])?? from?? YourTable??
group?? by?? (name?? +?? value))
方法2
delete?? a
from?? 表?? a?? left?? join(
select?? id=min(id)?? from?? 表?? group?? by?? name,value
)b?? on?? a.id=b.id
where?? b.id?? is?? null
查询及删除重复记录的SQL语句
查询及删除重复记录的SQL语句
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
)
?
学习sql有一段时间了，发现在我建了一个用来测试的表（没有建索引）中出现了许多的重复记录。后来总结了一些删除重复记录的方法，在Oracle中，可以通过唯一rowid实现删除重复记录；还可以建临时表来实现...这个只提到其中的几种简单实用的方法，希望可以和大家分享（以表employee为例）。
SQL> desc employee
Name????????????????????????????????????? Null???? Type
----------------------------------------- -------- ------------------
emp_id???????????????????????????????????????????? NUMBER(10)
emp_name?????????????????????????????????????????? VARCHAR2(20)
salary???????????????????????????????????????????? NUMBER(10,2)
?
可以通过下面的语句查询重复的记录：
?
SQL> select * from employee;
??? EMP_ID EMP_NAME????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon???????????????????????????????????????? 20000
???????? 2 semon???????????????????????????????????????? 20000
???????? 3 xyz?????????????????????????????????????????? 30000
???????? 2 semon???????????????????????????????????????? 20000
?
SQL> select distinct * from employee;
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon???????????????????????????????????????? 20000
???????? 3 xyz?????????????????????????????????????????? 30000
SQL> select * from employee group by emp_id,emp_name,salary having count (*)>1
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon???????????????????????????????????????? 20000
SQL> select * from employee e1
where rowid in (select max(rowid) from employe e2
where e1.emp_id=e2.emp_id and
e1.emp_name=e2.emp_name and e1.salary=e2.salary);
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 3 xyz?????????????????????????????????????????? 30000
???????? 2 semon???????????????????????????????????????? 20000
?
2. 删除的几种方法：
?
（1）通过建立临时表来实现
?
SQL>create table temp_emp as (select distinct * from employee)
SQL> truncate table employee; (清空employee表的数据）
?
SQL> insert into employee select * from temp_emp; (再将临时表里的内容插回来）
?
( 2）通过唯一rowid实现删除重复记录.在Oracle中，每一条记录都有一个rowid，rowid在整个数据库中是唯一的，rowid确定了每条记录是在Oracle中的哪一个数据文件、块、行上。在重复的记录中，可能所有列的内容都相同，但rowid不会相同，所以只要确定出重复记录中那些具有最大或最小rowid的就可以了，其余全部删除。
?
SQL>delete from employee e2 where rowid not in (
??????? select max(e1.rowid) from employee e1 where
??????? e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and e1.salary=e2.salary);--这里用min(rowid)也可以。
?
SQL>delete from employee e2 where rowid <(
??????? select max(e1.rowid) from employee e1 where
??????? e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and
????????????????? e1.salary=e2.salary);
（3）也是通过rowid，但效率更高。
?
SQL>delete from employee where rowid not in (
??????? select max(t1.rowid) from employee t1 group by
???????? t1.emp_id,t1.emp_name,t1.salary);--这里用min(rowid)也可以。
?
?
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 3 xyz?????????????????????????????????????????? 30000
???????? 2 semon???????????????????????????????????????? 20000
?
?
SQL> desc employee
Name????????????????????????????????????? Null???? Type
----------------------------------------- -------- ------------------
emp_id?????????????????????????????????????????????NUMBER(10)
emp_name?????????????????????????????????????????? VARCHAR2(20)
salary?????????????????????????????????????????????NUMBER(10,2)
?
可以通过下面的语句查询重复的记录：
?
SQL> select * from employee;
??? EMP_ID EMP_NAME????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon???????????????????????????????????????? 20000
???????? 2 semon???????????????????????????????????????? 20000
???????? 3 xyz?????????????????????????????????????????? 30000
???????? 2 semon???????????????????????????????????????? 20000
?
SQL> select distinct * from employee;
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon???????????????????????????????????????? 20000
???????? 3 xyz???????????????????????????????????????????30000
SQL> select * from employee group by emp_id,emp_name,salary having count (*)>1
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 2 semon?????????????????????????????????????????20000
SQL> select * from employee e1
where rowid in (select max(rowid) from employe e2
where e1.emp_id=e2.emp_id and
e1.emp_name=e2.emp_name and e1.salary=e2.salary);
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 3 xyz???????????????????????????????????????????30000
???????? 2 semon???????????????????????????????????????? 20000
?
2. 删除的几种方法：
?
（1）通过建立临时表来实现
?
SQL>create table temp_emp as (select distinct * from employee)
SQL> truncate table employee; (清空employee表的数据）
?
SQL> insert into employee select * from temp_emp; (再将临时表里的内容插回来）
?
( 2）通过唯一rowid实现删除重复记录.在Oracle中，每一条记录都有一个rowid，rowid在整个数据库中是唯一的，rowid确定了每条记录是在Oracle中的哪一个数据文件、块、行上。在重复的记录中，可能所有列的内容都相同，但rowid不会相同，所以只要确定出重复记录中那些具有最大或最小rowid的就可以了，其余全部删除。
?
SQL>delete from employee e2 where rowid not in (
??????? select max(e1.rowid) from employee e1 where
??????? e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and e1.salary=e2.salary);--这里用min(rowid)也可以。
?
SQL>delete from employee e2 where rowid <(
??????? select max(e1.rowid) from employee e1 where
??????? e1.emp_id=e2.emp_id and e1.emp_name=e2.emp_name and
????????????????? e1.salary=e2.salary);
（3）也是通过rowid，但效率更高。
?
SQL>delete from employee where rowid not in (
??????? select max(t1.rowid) from employee t1 group by
???????? t1.emp_id,t1.emp_name,t1.salary);--这里用min(rowid)也可以。
?
?
??? EMP_ID EMP_NAME???????????????????????????????????? SALARY
---------- ---------------------------------------- ----------
???????? 1 sunshine????????????????????????????????????? 10000
???????? 3 xyz???????????????????????????????????????????30000
???????? 2 semon???????????????????????????????????????? 20000