Array concatenation with distinct elements in BigQuery

Question

Let's say in each row I have an id and two arrays array_1 and array_2 that looks like following

SELECT 'a' id, [1,2,3,4,5] array_1, [2,2,2,3,6] array_2 UNION ALL
SELECT 'b', [2,3,4,5,6], [7,7,8,6,9] UNION ALL
SELECT 'c', [], [1,4,5]

I want concatenate these two arrays and only keep the unique elements in the new array. My desired output would look like the following

+----+-----------+-----------+-----------------------------+
| id |  array_1  |  array_2  | concatenated_array_distinct |
+----+-----------+-----------+-----------------------------+
| a  | 1,2,3,4,5 | 2,2,2,3,6 |                 1,2,3,4,5,6 |
| b  | 2,3,4,5,6 | 7,7,8,6,9 |             2,3,4,5,6,7,8,9 |
| c  |           |     1,4,5 |                       1,4,5 |
+----+-----------+-----------+-----------------------------+

I was trying to use array_concat function but I could not find a way to keep distinct elements using the array_concat function.

Is there anyway I can get the desired output?

Answer 1

Below is for BigQuery Standard SQL

... I was trying to use array_concat function but I could not find a way to keep distinct elements using the array_concat function. ...

You were on right track :o)

#standardSQL
WITH `project.dataset.table` AS (
  SELECT 'a' id, [1,2,3,4,5] array_1, [2,2,2,3,6] array_2 UNION ALL
  SELECT 'b', [2,3,4,5,6], [7,7,8,6,9] UNION ALL
  SELECT 'c', [], [1,4,5]
)
SELECT *, 
  ARRAY(SELECT DISTINCT x 
    FROM UNNEST(ARRAY_CONCAT(array_1, array_2)) x 
    ORDER BY x
  ) concatenated_array_distinct
FROM `project.dataset.table`  

Answer 2

You can use unnest() and union distinct:

with t as (
      select 'a' id, [1,2,3,4,5] array_1, [2,2,2,3,6] array_2 UNION ALL
      select 'b', [2,3,4,5,6], [7,7,8,6,9] UNION ALL
      select 'c', [], [1,4,5]
     )
select t.*,
       (select array_agg( e.el)
        from (select el
              from unnest(array_1) el
              union distinct 
              select el
              from unnest(array_2) el
             ) e 
       ) array_unique             
from t