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SQL重复记录查询---转

原创 Linux操作系统 作者:andyxu 时间:2010-07-01 15:33:58 0 删除 编辑

反复记录分为两种,第一种是完全反复的记录,也就是所有字段均反复的记录,第二种是部分要害字段反复的记录,例如Name字段反复,而其它字段不一定反复或都反复。

1、第一种反复很轻易解决,不同数据库环境下方法相似:

Mysql

create table tmp select distinct * from tableName;

drop table tableName;

create table tableName select * from tmp;

drop table tmp;

SQL Server

select distinct * into #Tmp from tableName;

drop table tableName;

select * into tableName from #Tmp;

drop table #Tmp;

Oracle

create table tmp as select distinct * from tableName;

drop table tableName;

create table tableName as select * from tmp;

drop table tmp;

发生这种反复的原因是由于表设计不周而产生的,增加唯一索引列就可以解决此问题。

2、此类反复问题通常要求保留反复记录中的第一条记录,操作方法如下。 假设有反复的字段为Name,Address,要求得到这两个字段唯一的结果集

Mysql

alter table tableName add autoID int auto_increment not null;

create table tmp select min(autoID) as autoID from tableName group by Name,Address;

create table tmp2 select tableName.* from tableName,tmp where tableName.autoID = tmp.autoID;

drop table tableName;

rename table tmp2 to tableName;

SQL Server

select identity(int,1,1) as autoID, * into #Tmp from tableName;

select min(autoID) as autoID into #Tmp2 from #Tmp group by Name,Address;

drop table tableName;

select * into tableName from #Tmp where autoID in(select autoID from #Tmp2);

drop table #Tmp;

drop table #Tmp2;

Oracle

DELETE FROM tableName t1 WHERE t1.ROWID > (SELECT MIN(t2.ROWID) FROM tableName t2 WHERE t2.Name = t1.Name and t2.Address = t1.Address);

说明:

1. MySQL和SQL Server中最后一个select得到了Name,Address不反复的结果集(多了一个autoID字段,在大家实际写时可以写在select子句中省去此列)

2. 因为MySQL和SQL Server没有提供rowid机制,所以需要通过一个autoID列来实现行的唯一性,而利用Oracle的rowid处理就方便多了。而且使用ROWID是最高效的删除反复记录方法

 

 

 

 

1、查找表中多余的反复记录,反复记录是根据单个字段(peopleId)来判定
select * from people
where peopleId in (select   peopleId  from   people  group  by   peopleId  having  count(peopleId) > 1)

2、删除表中多余的反复记录,反复记录是根据单个字段(peopleId)来判定,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、查找表中多余的反复记录(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、删除表中多余的反复记录(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、查找表中多余的反复记录(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”值存在反复的项;
Select Name,Count(*) From A Group By Name Having Count(*) > 1
假如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

  有两个意义上的反复记录,一是完全反复的记录,也即所有字段均反复的记录,二是部分要害字段反复的记录,比如Name字段反复,而其他字段不一定反复或都反复可以忽略。

  1、对于第一种反复,比较轻易解决,使用
select distinct * from tableName

  就可以得到无反复记录的结果集。

  假如该表需要删除反复的记录(反复记录保留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

  发生这种反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、这类反复问题通常要求保留反复记录中的第一条记录,操作方法如下

  假设有反复的字段为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不反复的结果集(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)查询反复
select * from tablename where id in (
select id from tablename 
group by id 
having count(id) > 1
)

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