建站教学网,让你建站更便捷和轻松!QQ交流群:78085540
您当前的位置:首页 > 网络编程 > 数据库综合

查询及删除重复记录的SQL语句

来源:建站教学网  时间:2010-08-12 16:49:30

查询及删除重复记录的sql语句

(一)
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


(二)
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 方法三

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)

方法四
查询重复
select * from tablename where id in (
select id from tablename
group by id
having count(id) > 1
)

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

补充

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)

责任编辑:admin

发表评论 共有条评论
用户名: 密码:
验证码: 匿名发表
CopyRight 2008-2009, JZREAD.COM, Inc. All Rights Reserved 联系QQ:568245346
皖ICP备09015033号