Posted on 2008-07-08 11:55
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Database
1. select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
----- ------ --------- ---- ----------- ---- ---- -------
7369 SMITH CLERK 7902 17-DEC-1980 800 20
7499 ALLEN SALESMAN 7698 20-FEB-1981 1600 300 30
7521 WARD SALESMAN 7698 22-FEB-1981 1250 500 30
7566 JONES MANAGER 7839 02-APR-1981 2975 20
7654 MARTIN SALESMAN 7698 28-SEP-1981 1250 1400 30
7698 BLAKE MANAGER 7839 01-MAY-1981 2850 30
7782 CLARK MANAGER 7839 09-JUN-1981 2450 10
7788 SCOTT ANALYST 7566 09-DEC-1982 3000 20
7839 KING PRESIDENT 17-NOV-1981 5000 10
7844 TURNER SALESMAN 7698 08-SEP-1981 1500 0 30
7876 ADAMS CLERK 7788 12-JAN-1983 1100 20
7900 JAMES CLERK 7698 03-DEC-1981 950 30
7902 FORD ANALYST 7566 03-DEC-1981 3000 20
7934 MILLER CLERK 7782 23-JAN-1982 1300 10
2.问题：查找DEPTNO 20中出现最多次数的工资？
select sal
from emp
where deptno = 20
order by sal
SAL
----------
800
1100
2975
3000
3000
3.解决方案
使用窗口函数 DENSE_RANK,把工资重复出现的次数分等级。
1 select sal
2 from (
3 select sal,
4 dense_rank()over( order by cnt desc) as rnk
5 from (
6 select sal, count(*) as cnt
8 from emp
9 where deptno = 20
10 group by sal
11 ) x
12 ) y
13 where rnk = 1