使用MySQL中的AVG函数求平均值的教程

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)

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

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)