MySQL的AVG函數用來查找各種記錄的一個字段的平均值。
為了理解AVG函數,考慮有一個employee_tbl表,其具有以下記錄:
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)
現在,假設在上述表的基礎上計算所有dialy_typing_pages的平均值,那麼可以使用下面的命令:
mysql> SELECT AVG(daily_typing_pages) -> FROM employee_tbl; +-------------------------+ | AVG(daily_typing_pages) | +-------------------------+ | 230.0000 | +-------------------------+ 1 row in set (0.03 sec)
使用 GROUP BY 子句設置各種記錄的平均值。下面的例子將涉及到單個人的記錄將有每個人的平均值打印出來。
mysql> 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)