MySQL的AVG函式用來查詢各種記錄的一個欄位的平均值。
為了理解AVG函式，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 子句設定各種記錄的平均值。下面的例子將涉及到單個人的記錄將有每個人的平均值列印出來。
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)