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Oracle中from中子查询实例应用

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Release: 2016-06-07 17:23:55
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Oracle表复杂查询
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字查询
from 中的子查询

例子:如何显示高于自己部门平均工工资的员工信息
思路:


1.查询出各个部门的平均工资和部门号


select deptno, avg(sal) mysal from emp group bydeptno;


2.把上面的查询结果看作是一张子表


select a2.ename ,a2.sal,a2.deptno ,a1.mysal from emp a2

(select deptno, avg(sal) mysal from emp group bydeptno) a1

where a2.deptno=a1.deptno and a2.sal >a1.mysal


这里需要说明的是当from字句中使用子查询时,,该子查询会被作为一个视图来对待,因此叫做内嵌视图,当在From字句中使用子查询时,必须给予查询指定别名。
别名不建议用as

linux

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