由於MYSQL沒有提供類似ORACLE中OVER()這樣豐富的分析函式. 所以在MYSQL裡需要實現這樣的功能,我們只能用一些靈活的辦法:[@more@]

1.首先我們來建立例項資料:

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. 確定需求: 根據部門來分組,顯示各員工在部門裡按薪水排名名次.

顯示結果預期如下:

+-------+--------+----------+------+
| 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 實現

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. 結果演示

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)

5.小結
此SQL正是利用了MYSQL的靈活以及使用者變數的呼叫. 希望大家可以透過此例舉一反三.寫出更多更精彩的SQL.

MYSQL-實現ORACLE- row_number() over(partition by ) 分組排序功能.

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