MySQL实现分组排序（8.0版本以下ROW_NUMBER() OVER()）

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)  
 
 
 
MySql中取出每个分组中的前N条记录   
select a1.* from article a1   
 
inner join   
 
(select a.type,a.date from article a left join article b   
 
on a.type=b.type and a.date<=b.date    
 
group by a.type,a.date   
 
having count(b.date)<=2  
 
)b1   
 
on a1.type=b1.type and a1.date=b1.date  
 
order by a1.type,a1.date desc