AVG() 函数

AVG() 函数

AVG() 函数返回数值列的平均值。

语法

SELECT AVG(column_name) FROM table_name

示例

示例使用样本数据库。

"access_log" 表：

+-----+---------+-------+------------+
| aid | site_id | count | date       |
+-----+---------+-------+------------+
|   1 |       1 |    45 | 2016-05-10 |
|   2 |       3 |   100 | 2016-05-13 |
|   3 |       1 |   230 | 2016-05-14 |
|   4 |       2 |    10 | 2016-05-14 |
|   5 |       5 |   205 | 2016-05-14 |
|   6 |       4 |    13 | 2016-05-15 |
|   7 |       3 |   220 | 2016-05-15 |
|   8 |       5 |   545 | 2016-05-16 |
|   9 |       3 |   201 | 2016-05-17 |
+-----+---------+-------+------------+

从 "access_log" 表的 "count" 列获取平均值：

SELECT AVG(count) AS CountAverage FROM access_log;

输出结果：

mysql> SELECT AVG(count) AS CountAverage FROM access_log;

+--------------+
| CountAverage |
+--------------+
|  174.3333    |
+--------------+

选择访问量高于平均访问量的 "site_id" 和 "count"：

SELECT site_id, count FROM access_log
WHERE count > (SELECT AVG(count) FROM access_log);

输出结果：

mysql> SELECT site_id, count FROM access_log
    -> WHERE count > (SELECT AVG(count) FROM access_log);

+---------+-------+
| site_id | count |
+---------+-------+
|       1 |   230 | 
|       5 |   205 | 
|       3 |   220 | 
|       5 |   545 | 
|       3 |   201 | 
+---------+-------+