# **SUM**

## **函数说明**

`SUM()` 聚合函数用于计算一组值的和（NULL 值被忽略）。

## **函数语法**

```text
> SUM(expr)
```

## **参数释义**

|  参数  | 说明 |
|  ----  | ----  |
| expr  | 任何数值类型与字符串列的列名|

## **返回值**

返回 `expr` 列的数值的和，若输入参数为 `Double` 类型，则返回值为 `Double`，否则为整数类型。
如果没有匹配的行，则返回 `NULL` 值。

## **示例**

```text
> 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 sum(col_1c) from tbl1;
+-------------+
| sum(col_1c) |
+-------------+
|          21 |
+-------------+

> select sum(col_1d) as c1 from tbl1 where col_1d < 13 group by col_1e order by c1;
+------+
| c1   |
+------+
|    8 |
|   10 |
|   18 |
|   21 |
+------+
```