AVG函數(shù)用于找出表中記錄在某字段處的平均值。

要理解 AVG 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 的平均值，那么你可以用如下命令來達到目的：

    SQL> SELECT AVG(daily_typing_pages)
        -> FROM employee_tbl;
    +-------------------------+
    | AVG(daily_typing_pages) |
    +-------------------------+
    |                230.0000 |
    +-------------------------+
    1 row in set (0.03 sec)

你還可以使用 GROUP BY 子句來計算不同記錄分組的平均值。下面的例子將會計算得出每個人平均值，你將能夠得到平均每個人每天打的頁數(shù)。

    SQL> SELECT name, AVG(daily_typing_pages)
        -> FROM employee_tbl GROUP BY name;
    +------+-------------------------+
    | name | AVG(daily_typing_pages) |
    +------+-------------------------+
    | Jack |                135.0000 |
    | Jill |                220.0000 |
    | John |                250.0000 |
    | Ram  |                220.0000 |
    | Zara |                325.0000 |
    +------+-------------------------+
    5 rows in set (0.20 sec)