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
