# AVG

## 函数说明

`AVG()` 是聚合函数的一种，用于计算参数列的算术平均值。

## 函数语法

``````> AVG(expr)
``````

expr 任何数值类型的列的列名

## 返回值

`Double` 类型返回该列的算术平均值。 若输入参数为空，则返回 `NaN` 值。

## 示例

``````> drop table if exists tbl1,tbl2;
> create table tbl1 (col_1a tinyint, col_1b smallint, col_1c int, col_1d bigint, col_1e char(10) not null);
> insert into tbl1 values (0,1,1,7,"a");
> insert into tbl1 values (0,1,2,8,"b");
> insert into tbl1 values (0,1,3,9,"c");
> insert into tbl1 values (0,1,4,10,"D");
> insert into tbl1 values (0,1,5,11,"a");
> insert into tbl1 values (0,1,6,12,"c");

> select avg(col_1c) from tbl1;
+-------------+
| avg(col_1c) |
+-------------+
|      3.5000 |
+-------------+

> select sum(col_1d) as s1,avg(col_1d) as a3 from tbl1 group by col_1e order by s1 desc;
+------+---------+
| s1   | a3      |
+------+---------+
|   21 | 10.5000 |
|   18 |  9.0000 |
|   10 | 10.0000 |
|    8 |  8.0000 |
+------+---------+

> select avg(col_1d) as a1 from tbl1 where col_1d < 13 group by col_1e order by a1;
+---------+
| a1      |
+---------+
|  8.0000 |
|  9.0000 |
| 10.0000 |
| 10.5000 |
+---------+
``````