今天有人問max() over()的需求在mysql中怎麼寫。
同以前講過的幾個例子一樣，雖然mysql中沒有分析函數，可max() over()的方法一樣很容易實現
max() over()
mysql> set @max_sal=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select if(@max_sal=0,@max_sal:=sal,@max_sal) as max_sal,sal from emp order by sal desc;
+---------+------+
| max_sal | sal |
+---------+------+
| 5000 | 5000 |
| 5000 | 3000 |
| 5000 | 3000 |
| 5000 | 2975 |
| 5000 | 2850 |
| 5000 | 2450 |
| 5000 | 1600 |
| 5000 | 1500 |
| 5000 | 1300 |
| 5000 | 1250 |
| 5000 | 1250 |
| 5000 | 1100 |
| 5000 | 950 |
| 5000 | 800 |
+---------+------+
14 rows in set (0.00 sec)max() over(partition)
mysql> set @deptno=0,@max_sal=0;
Query OK, 0 rows affected (0.00 sec)
mysql> select @deptno,if(@deptno=deptno,@max_sal,@max_sal:=sal) as max_sal,deptno,sal,@deptno:=deptno from emp order by deptno,sal desc;
+---------+---------+--------+------+-----------------+
| @deptno | max_sal | deptno | sal | @deptno:=deptno |
+---------+---------+--------+------+-----------------+
| 0 | 5000 | 10 | 5000 | 10 |
| 10 | 5000 | 10 | 2450 | 10 |
| 10 | 5000 | 10 | 1300 | 10 |
| 10 | 3000 | 20 | 3000 | 20 |
| 20 | 3000 | 20 | 3000 | 20 |
| 20 | 3000 | 20 | 2975 | 20 |
| 20 | 3000 | 20 | 1100 | 20 |
| 20 | 3000 | 20 | 800 | 20 |
| 20 | 2850 | 30 | 2850 | 30 |
| 30 | 2850 | 30 | 1600 | 30 |
| 30 | 2850 | 30 | 1500 | 30 |
| 30 | 2850 | 30 | 1250 | 30 |
| 30 | 2850 | 30 | 1250 | 30 |
| 30 | 2850 | 30 | 950 | 30 |
+---------+---------+--------+------+-----------------+
14 rows in set (0.00 sec)