MySQL中的SUM函数使用教程

mysql的sum函数是用来找出记录中各种的字段的总和。

要了解sum函数考虑employee_tbl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，假设根据上面的表想来计算所有的dialy_typing_pages的总数，那么可以通过使用下面的命令：

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子句设置的各种记录的总和。下面的例子将总结所有相关的记录一个人，打印纸的每一个人总数。

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)