MYSQL怎么实现分组排序功能

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由于MYSQL没有提供类似ORACLE中OVER()这样丰富的分析函数. 所以在MYSQL里需要实现这样的功能,我们只能用一些灵活的办法:

1.首先我们来创建实例数据:

drop table if exists heyf_t10;
create table heyf_t10 (empid int ,deptid int ,salary decimal(10,2) );

insert into heyf_t10 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);

2. 确定需求: 根据部门来分组,显示各员工在部门里按薪水排名名次.

显示结果预期如下:

+-------+--------+----------+------+
| 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 |
+-------+--------+----------+------+

3. SQL 实现

select empid,deptid,salary,rank from (
select heyf_tmp.empid,heyf_tmp.deptid,heyf_tmp.salary,@rownum:=@rownum+1 ,
if(@pdept=heyf_tmp.deptid,@rank:=@rank+1,@rank:=1) as rank,
@pdept:=heyf_tmp.deptid
from (
select empid,deptid,salary from heyf_t10 order by deptid asc ,salary desc
) heyf_tmp ,(select @rownum :=0 , @pdept := null ,@rank:=0) a ) result
;

4. 结果演示

mysql> select empid,deptid,salary,rank from (
   -> select heyf_tmp.empid,heyf_tmp.deptid,heyf_tmp.salary,@rownum:=@rownum+1 ,
   -> if(@pdept=heyf_tmp.deptid,@rank:=@rank+1,@rank:=1) as rank,
   -> @pdept:=heyf_tmp.deptid
   -> from (
   -> select empid,deptid,salary from heyf_t10 order by deptid asc ,salary desc
   -> ) heyf_tmp ,(select @rownum :=0 , @pdept := null ,@rank:=0) a ) result
   ->  ;
+-------+--------+----------+------+
| 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 |
+-------+--------+----------+------+
9 rows in set (0.00 sec)