注册 登录  
 加关注
   显示下一条  |  关闭
温馨提示!由于新浪微博认证机制调整,您的新浪微博帐号绑定已过期,请重新绑定!立即重新绑定新浪微博》  |  关闭

沉默蜂B4A安卓编程

国内资料最全的B4A资料库

 
 
 

日志

 
 

[转帖]sql语句删除重复的记录的方法  

2014-04-19 14:21:05|  分类: B.ASP与SQL |  标签: |举报 |字号 订阅

  下载LOFTER 我的照片书  |

来源  《 sql语句删除重复的记录的方法  》


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)   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

  评论这张
 
阅读(231)| 评论(0)
推荐 转载

历史上的今天

在LOFTER的更多文章

评论

<#--最新日志,群博日志--> <#--推荐日志--> <#--引用记录--> <#--博主推荐--> <#--随机阅读--> <#--首页推荐--> <#--历史上的今天--> <#--被推荐日志--> <#--上一篇,下一篇--> <#-- 热度 --> <#-- 网易新闻广告 --> <#--右边模块结构--> <#--评论模块结构--> <#--引用模块结构--> <#--博主发起的投票-->
 
 
 
 
 
 
 
 
 
 
 
 
 
 

页脚

网易公司版权所有 ©1997-2017