常用三种数据库(sql service,mysql ,oracle)的数据备份
--数据备份
--oracle
create table studentback
as
select *from student
--mysql
create table studentback
select *from student
--SQL service
select *into studentback
from student
--查询4-6条数据库
select *from
（
select temp.*,rownum rn from
(
select *from student
)temp
where rownum<=6
）where rn >=4
--查询id=2的用户的数据
select *from
（
select name,age,address,rownum rn from student
）temp
where rn=2
--查询name，age均不重复的数据记录
--利用分组 获取信息
select name,age,count(name|| age) from student
group by name,age
having (count(name|| age)<2)
--查询不重复的学生信息
select distinct id,name,age,address from student