MySQL的SUM函數(shù)是用來(lái)找出記錄中各種的字段的總和。
要了解SUM函數(shù)考慮EMPLOYEE_TBL表具有以下記錄：
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)
現(xiàn)在，假設(shè)根據(jù)上面的表想來(lái)計(jì)算所有的dialy_typing_pages的總數(shù)，那么可以通過(guò)使用下面的命令：
mysql> SELECT SUM(daily_typing_pages) -> FROM employee_tbl;+-------------------------+| SUM(daily_typing_pages) |+-------------------------+| 1610 |+-------------------------+1 row in set (0.00 sec)
可以使用GROUP BY子句設(shè)置的各種記錄的總和。下面的例子將總結(jié)所有相關(guān)的記錄一個(gè)人，打印紙的每一個(gè)人總數(shù)。
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)
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