select b.job from dept a,emp b where a.deptno=b.deptno and a.deptno in (10,20)
minus
(select b.job from dept a,emp b where a.deptno=b.deptno and a.deptno=10
intersect
select b.job from dept a,emp b where a.deptno=b.deptno and a.deptno=20);
minus
(select b.job from dept a,emp b where a.deptno=b.deptno and a.deptno=10
intersect
select b.job from dept a,emp b where a.deptno=b.deptno and a.deptno=20);
select job from emp where deptno in (10,20)
MINUS
(select job from emp where deptno=10
INTERSECT
select job from emp where deptno=20);
二楼的思路是怎么样的呢?