用PostgreSQL给的例子，可以看得比较清楚：
SELECT
depname,
empno,
salary,
rank() OVER (PARTITION BY depname ORDER BY salary DESC)
FROM empsalary;
depname | empno | salary | rank
-----------+-------+--------+------
develop | 8 | 6000 | 1
develop | 10 | 5200 | 2
develop | 11 | 5200 | 2
develop | 9 | 4500 | 4
develop | 7 | 4200 | 5
personnel | 2 | 3900 | 1
personnel | 5 | 3500 | 2
sales | 1 | 5000 | 1
sales | 4 | 4800 | 2
sales | 3 | 4800 | 2
(10 rows)
本文转自健哥的数据花园博客园博客，原文链接：http://www.cnblogs.com/gaojian/archive/2012/09/06/2672982.html，如需转载请自行联系原作者
