当我们将 MySQL SUM() 函数与 GROUP BY 子句一起使用时，SUM() 函数会计算 GROUP BY 子句中指定的每个组的总和。将 SUM() 与 GROUP BY 子句一起使用的好处是我们可以轻松找到特定组的总计。要理解上述概念，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)

以下查询将汇总与一个人相关的所有记录，您将获得每个人输入的总页数。

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)