SQL SUM 函數(shù)

SQL SUM 函數(shù)

SUM函數(shù)用于找出表中記錄在某字段處的總和。

要理解 SUM 函數(shù)，請考慮 employee_tbl 表，表中記錄如下所示：

    SQL> 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，假設你想要獲取 daily_typing_pages 的總和，那么你可以用如下命令來達到目的：

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

你還可以使用 GROUP BY 子句來得出不同記錄分組的總和。下面的例子將會計算得出每個人的總和，，你將能夠得到每個人每天打的總頁數(shù)。

    SQL> SELECT name, SUM(daily_typing_pages)
        -> FROM employee_tbl GROUP BY name;