AVG()

AVG() 函数返回数值列的平均值。

1. 实例

查询课程表courses，计算表中学生上课人数student_count的平均值

SELECT AVG(student_count) AS average_student_count
FROM courses;

执行输出结果

mysql> SELECT AVG(student_count) AS average_student_count
    -> FROM courses;
+---------------------------+
| average_student_count |
+---------------------------+
|                  929.0000 |
+---------------------------+
1 row in set (0.00 sec)

其中AS相当于给AVG(student_count)取了个显示在列表中的别名

练习题：AVG

题目描述：查询教师表teachers中教师邮箱为’qq.com‘结尾的年龄的平均值

SELECT AVG(age)
FROM teachers
WHERE email LIKE '[e-mail]';

目标输出结果

mysql> SELECT AVG(age)
    -> FROM teachers
    -> WHERE email LIKE '[e-mail]';
+----------+
| AVG(age) |
+----------+
|  21.0000 |
+----------+
1 row in set (0.00 sec)