查询以从 array_aggregate 获取数据答案

【问题标题】：Query to fetch data from array_aggregate查询以从 array_aggregate 获取数据
【发布时间】：2022-01-21 22:25:24
【问题描述】：

我在数组中有包含数据的列。

Alphabets    
{A,B,C}
{A}
{B,C}

我需要一个查询，它给我输出为 {A} 的 A

【问题讨论】：

标签： presto

【解决方案1】：

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() 来减少处理时间和数据传输，而不是使用 sum() 和 UNNEST，如下例所示。

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;

任一查询都返回以下结果。返回结果的顺序不保证。

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

参考：

https://docs.aws.amazon.com/athena/latest/ug/arrays-and-aggregation.html

【讨论】：