A.A UNION B B.A UNION ALL B C.A INTERSECT B D.A MIUS B
A.A MIUS B B.B MINUS A C.A INTERSECT B D.B INTERSECT A
A.select job from emp; B.select job,count(*) from emp; C.select distinct job,count(*) from emp; D.select job,count(*) from emp group by job; E.select job,sum(empno) from emp group by job;