SQL MAX函数被用来找出记录集合中的最大值的记录。

理解MAX()函数，考虑一个employee_tbl表，其具有以下记录：

SQL> 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)

现在假设想要取daily_typing_pages的最大值在上述表中，那么可以这样做简单地使用下面的命令：

SQL> SELECT MAX(daily_typing_pages)
    -> FROM employee_tbl;
+-------------------------+
| MAX(daily_typing_pages) |
+-------------------------+
|                     350 |
+-------------------------+
1 row in set (0.00 sec)

可以找到所有使用GROUP BY子句，如下每个名称最大值记录：

SQL> SELECT id, name, MAX(daily_typing_pages)
    -> FROM employee_tbl GROUP BY name;
+------+------+-------------------------+
| id   | name | MAX(daily_typing_pages) |
+------+------+-------------------------+
|    3 | Jack |                     170 |
|    4 | Jill |                     220 |
|    1 | John |                     250 |
|    2 | Ram  |                     220 |
|    5 | Zara |                     350 |
+------+------+-------------------------+
5 rows in set (0.00 sec)

您可以使用MIN()函数找出最小值以及MAX()函数找出最大值，试试下面的例子：

SQL> 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)