Compare array against array column in postgres - postgresql

Question

# things :string is an Array
scope :things, ->(q) { where('ARRAY[?]::varchar[] IN things', Array.wrap(q)) }
scope :things, ->(q) { where('things && ARRAY[?]::varchar[]', Array.wrap(q)) }
scope :things, ->(q) { where('ARRAY[?]::varchar[] <# things', Array.wrap(q)) }
I've tried a few versions, but I can't seem to find the proper incantation. I'm looking to find any row that has any of the things in the array... is there any overlap?
[1, 2, 3] & [1, 8] = t
[1, 2, 3] & [8, 9] = f
I'm trying to mimic ActiveRecord's default where behavior. If I give it an array, it'll get all the matching rows. Is this possible with postgres arrays? Is it even efficient?

Answer 1

One way of doing this is by converting the arrays to a set of rows. Once you have the arrays as set of rows, you can do an intersection between them and check if the result is empty set.
For example:
CREATE TABLE my_test_table(id BIGINT, test_array BIGINT[]);
INSERT INTO my_test_table(id, test_array)
VALUES
(1, array[1,2,3]),
(2, ARRAY[1,5,8]);
SELECT * FROM my_test_table
WHERE array_length((SELECT array
(
SELECT UNNEST(test_array)
INTERSECT
SELECT UNNEST(array[3,15,2])
)), 1) > 0;
The result of the SELECT statement above is:
1 | {1,2,3}
This allows for more complex matching of elements of 2 arrays. For example, if you would like to select the arrays that have at least 2 common elements, you could just change the WHERE part to
WHERE array_length((SELECT array
(
SELECT UNNEST(test_array)
INTERSECT
SELECT UNNEST(array[3,15,2])
)), 1) > 1;