MySQL SUM 函数

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  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)