oracle简单创建视图

1.平均薪水的等级最低的部门的部门名称:

select dname from
(
    select avg_sal, deptno, grade from (select avg(sal) avg_sal,deptno from emp group by deptno)
    join salgrade on avg_sal between salgrade.losal and salgrade.hisal
) t1
join dept on t1.deptno=dept.deptno
where t1.grade=
(
    select min(grade) from
    (
        select avg_sal, deptno, grade from (select avg(sal) avg_sal,deptno from emp group by deptno)
        join salgrade on avg_sal between salgrade.losal and salgrade.hisal
    )
)

对于比较繁琐的select语句，可以通过建立一个视图作为一张表，来简化sql语句，是语句的可读性更强一些：

2.创建视图：
create view v$_dept_avg_sal_info as
select avg_sal, deptno, grade from (select avg(sal) avg_sal,deptno from emp group by deptno)
join salgrade on avg_sal between salgrade.losal and salgrade.hisal

（解释：

 　　　create view 固定语句；

　　　 v$_dept_avg_sal_info 为视图名称；

　　    as 固定语句；

　　    select avg_sal, deptno, grade from (select avg(sal) avg_sal,deptno from emp group by deptno)
　　    join salgrade on avg_sal between salgrade.losal and salgrade.hisal 要创建视图的sql数据

）

3.执行--》视图创建好了，之后上面比较繁琐的sql文可以写成如下的样子了：

select dname, t1.deptno, grade, avg_sal from
v$_dept_avg_sal_info t1
join dept on (t1.deptno=dept.deptno)
where t1.grade=
(
select min(grade) from v$_dept_avg_sal_info
)