oracle如何全量去重,oracle怎么去重效率高

oracle如何去重?

C列也要考虑对么?

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delete from table x

where not exists (select 1 from (select a,b,max(c) c from table group by a,b ) y

where x.a=y.a and x.b=y.b and x.c=y.c);

随机删除重复列:

delete from table x

where exists(select 1 from (select a, b, max(rowid) max_rowid from table group by a, b) y

where x.a=y.a and x.b=y.b and x.rowid y.max_rowid);

oracle 批量插入时,如何去除重复数据

先去重再导入。

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 表 a

where (a.Id,a.seq) in

(select Id,seq from 表 group by Id,seq having count(*) 1)

and rowid not in

(select min(rowid) from 表 group by Id,seq having count(*)1)

Oracle查询去除重数据

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;


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