Use aggregation functions with arrays

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Use aggregation functions with arrays - Amazon Athena

To add values within an array, use SUM, as in the following example.
To aggregate multiple rows within an array, use array_agg. For information, see Create arrays from subqueries.

Note

ORDER BY is supported for aggregation functions starting in Athena engine version 2.


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;

In the last SELECT statement, instead of using sum() and UNNEST, you can use reduce() to decrease processing time and data transfer, as in the following example.


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;

Either query returns the following results. The order of returned results is not guaranteed.


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