# 将聚合函数与数组结合使用
<a name="arrays-and-aggregation"></a>
+ 要在数组中添加值，请使用 `SUM`，如以下示例所示。
+ 要在数组中聚合多个行，请使用 `array_agg`。有关信息，请参阅[从子查询创建数组](creating-arrays-from-subqueries.md)。

**注意**  
从 Athena 引擎版本 2 开始的聚合函数支持 `ORDER BY`。

```
WITH
dataset AS (
  SELECT ARRAY
  [
    ARRAY[1,2,3,4],
    ARRAY[5,6,7,8],
    ARRAY[9,0]
  ] AS items
),
item AS (
  SELECT i AS array_items
  FROM dataset, UNNEST(items) AS t(i)
)
SELECT array_items, sum(val) AS total
FROM item, UNNEST(array_items) AS t(val)
GROUP BY array_items;
```

在最后一个 `SELECT` 语句中，您可以使用 `reduce()` 而不是 `sum()` 和 `UNNEST` 来减少处理时间和数据传输，如以下示例所示。

```
WITH
dataset AS (
  SELECT ARRAY
  [
    ARRAY[1,2,3,4],
    ARRAY[5,6,7,8],
    ARRAY[9,0]
  ] AS items
),
item AS (
  SELECT i AS array_items
  FROM dataset, UNNEST(items) AS t(i)
)
SELECT array_items, reduce(array_items, 0 , (s, x) -> s + x, s -> s) AS total
FROM item;
```

任一查询返回以下结果。不保证返回结果的顺序。

```
+----------------------+
| array_items  | total |
+----------------------+
| [1, 2, 3, 4] | 10    |
| [5, 6, 7, 8] | 26    |
| [9, 0]       | 9     |
+----------------------+
```