MySQL SUM 函数

  • SUM 函数

    MySQL SUM函数用于找出各种记录中一个字段的总和。要了解SUM函数,请考虑一个employee_tbl表,该表具有以下记录-
    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,假设基于上表您要计算所有Dialy_typing_pages的总数,那么您可以使用以下命令进行计算
    mysql> SELECT SUM(daily_typing_pages)
       -> FROM employee_tbl;
    +-------------------------+
    | SUM(daily_typing_pages) |
    +-------------------------+
    |          1610           |
    +-------------------------+
    1 row in set (0.00 sec)
    您可以使用GROUP BY子句获取各种记录集的总和。以下示例将汇总与一个人相关的所有记录,并且您将拥有每个人的总打字页面。
    mysql> SELECT name, SUM(daily_typing_pages)
       -> FROM employee_tbl GROUP BY name;
    +------+-------------------------+
    | name | SUM(daily_typing_pages) |
    +------+-------------------------+
    | Jack |           270           |
    | Jill |           220           |
    | John |           250           |
    | Ram  |           220           |
    | Zara |           650           |
    +------+-------------------------+
    5 rows in set (0.17 sec)