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)
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