建立雇員表：
create table emp(deptno number(10),ename varchar2(100),sal number(10,2))；
插入資料
begin
insert into emp values('10','king',5000);
insert into emp values('10','clark',2450);
insert into emp values('10','miller',1300);
insert into emp values('20','scott',3000);
insert into emp values('20','ford',3000);
insert into emp values('20','jones',2975);
insert into emp values('20','adams',1100);
insert into emp values('20','smith',800);
insert into emp values('30','blake',2850);
insert into emp values('30','allen',1600);
insert into emp values('30','turner',1500);
insert into emp values('30','ward',1250);
insert into emp values('30','martin',1250);
insert into emp values('30','james',950);
commit;
end;
1、使用row_number()、rank()、dense_rank()查出各部門薪水最高的三個員工姓名、薪水，多於三個的只取三個。
select *
from (select e.deptno,
e.ename,
e.sal,
row_number()over(partition by e.deptno order by sal desc) rankno
from emp e)
where rankno <= 3;
select *
from (select e.deptno,
e.ename,
e.sal,
rank()
over(partition by e.deptno order by sal desc) rankno
from emp e)
where rankno <= 3;
select *
from (select e.deptno,
e.ename,
e.sal,
row_number()
over(partition by e.deptno order by sal desc) rankno
from emp e)
where rankno <= 3;
select *
from (select e.deptno,
e.ename,
e.sal,
dense_rank()
over(partition by e.deptno order by sal desc) rankno
from emp e)
where rankno <= 3;
注：row_number()排名的名次不會出現重複;rank（）則會出現排名名次相同且如果兩人的名次都為2，則下個人的名次則為4而不是為3，而dense_rank（）則與rank()恰好相反。
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