将 MySQL SUM() 函数与 GROUP BY 子句结合使用有什么好处?
mysqlmysqli database更新于 2024/3/14 9:15:00
当我们将 MySQL SUM() 函数与 GROUP BY 子句结合使用时，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 子句结合使用的好处是，我们可以轻松找到特定组的总数。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)
以下查询将汇总与单个人相关的所有记录，并且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)
