发布于 2016-04-01 02:44:34 | 176 次阅读 | 评论: 0 | 来源: 网友投递
Mysql关系型数据库管理系统
MySQL是一个开放源码的小型关联式数据库管理系统,开发者为瑞典MySQL AB公司。MySQL被广泛地应用在Internet上的中小型网站中。由于其体积小、速度快、总体拥有成本低,尤其是开放源码这一特点,许多中小型网站为了降低网站总体拥有成本而选择了MySQL作为网站数据库。
MySQL的max()函数是用来找出一个记录集中的最大值记录。
要了解MAX功能考虑的EMPLOYEE_TBL表具有以下记录:
mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 3 | Jack | 2007-04-06 | 100 |
| 4 | Jill | 2007-04-06 | 220 |
| 5 | Zara | 2007-06-06 | 300 |
| 5 | Zara | 2007-02-06 | 350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)
现在,假设根据上述要取表中daily_typing_pages的最大值值,简单地使用下面的命令:
mysql> SELECT MAX(daily_typing_pages)
-> FROM employee_tbl;
+-------------------------+
| MAX(daily_typing_pages) |
+-------------------------+
| 350 |
+-------------------------+
1 row in set (0.00 sec)
可以找到所有的记录,最大值为每名使用GROUP BY子句如下:
mysql> SELECT id, name, work_date, MAX(daily_typing_pages)
-> FROM employee_tbl GROUP BY name;
+------+------+------------+-------------------------+
| id | name | work_date | MAX(daily_typing_pages) |
+------+------+------------+-------------------------+
| 3 | Jack | 2007-05-06 | 170 |
| 4 | Jill | 2007-04-06 | 220 |
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 5 | Zara | 2007-06-06 | 350 |
+------+------+------------+-------------------------+
5 rows in set (0.00 sec)
也可以使用MIN函数及MAX功能找到的最低值,试试下面的例子:
mysql> SELECT MIN(daily_typing_pages) least, MAX(daily_typing_pages) max
-> FROM employee_tbl;
+-------+------+
| least | max |
+-------+------+
| 100 | 350 |
+-------+------+
1 row in set (0.01 sec)