删除重复数据的几个方法 -电脑资料

删除重复数据的几个方法

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......)

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，

电脑资料

create table table_new as select distinct * from table1 minux

truncate table table1;

insert into table1 select * from table_new;