sql语句实例析解

部门：dept(deptno,dname)

员工：emp(ename,sal,deptno)

薪资等级：salgrade(grade,losal,hisal)

 平均工资的最小值及部门编号和工资等级及部门名称：

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