Mysql——分组排序加序列号

CREATE TABLE IF NOT EXISTS `employee` (
`empid` int(11) DEFAULT NULL,
`deptid` int(11) DEFAULT NULL,
`salary` decimal(10,2) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
INSERT INTO `employee` (`empid`, `deptid`, `salary`) VALUES
(1, 10, 5500.00),
(2, 10, 4500.00),
(3, 20, 1900.00),
(4, 20, 4800.00),
(5, 40, 6500.00),
(6, 40, 14500.00),
(7, 40, 44500.00),
(8, 50, 6500.00),
(9, 50, 7500.00);

<span style="font-family: Monaco, Consolas, Courier, 'Lucida Console', monospace; font-size: 14px; line-height: 21px; white-space: pre; widows: auto;">是这样的我想实现新加一列代表每个部门的工资等级，比如</span><pre name="code" class="sql">+-------+--------+----------+
| empid | deptid | salary   |
+-------+--------+----------+
|     1 |     10 |  5500.00 |
|     2 |     10 |  4500.00 |
|     3 |     20 |  1900.00 |
|     4 |     20 |  4800.00 |
|     5 |     40 |  6500.00 |
|     6 |     40 | 14500.00 |
|     7 |     40 | 44500.00 |
|     8 |     50 |  6500.00 |
|     9 |     50 |  7500.00 |
+-------+--------+----------+
//实现下面结果
empid       deptid      salary         rank
+-------+--------+----------+------+--------
1           10          5500.00        1
2           10          4500.00        2
4           20          4800.00        1
3           20          1900.00        2
7           40          44500.00       1
6           40          14500.00       2
5           40          6500.00        3
9           50          7500.00        1
8           50          6500.00        2

SELECT empid,deptid,salary,rank FROM
(SELECT *,@rownum:=@rownum+1 AS rownum,IF(@pa=ff.deptid,@rank:=@rank+1,@rank:=1) AS rank,@pa:=ff.deptid
FROM
(SELECT empid,deptid,salary FROM employee GROUP BY deptid,salary ORDER BY deptid ASC, salary DESC) ff,(SELECT @rank:=0,@rownum:=0,@pa=NULL) tt) result