MySQL SUM 函数用于计算多条记录中某个字段的总和。要理解 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，假设根据上表您想要计算所有 dialy_typing_pages 的总数，那么您可以使用以下命令来完成 -

mysql> SELECT SUM(daily_typing_pages)    -> FROM employee_tbl;+-------------------------+| SUM(daily_typing_pages) |+-------------------------+|         1610            |+-------------------------+1 row in set (0.00 sec)