How to compare two arrays and pick only the non matching elements In postgres

Question

How can I pick only the non matching elements between two arrays.

Example:

base_array [12,3,5,7,8]
temp_array [3,7,8]

So here I wan

Answer 1

I would create a function using the same except logic as described by @a_horse_with_no_name:

CREATE FUNCTION array_subtract(a1 int[], a2 int[]) RETURNS int[] AS $$
DECLARE
    ret int[];
BEGIN
    IF a1 is null OR a2 is null THEN
        return a1;
    END IF;
    SELECT array_agg(e) INTO ret
    FROM (
        SELECT unnest(a1)
        EXCEPT
        SELECT unnest(a2)
    ) AS dt(e);
    RETURN ret;
END;
$$ language plpgsql;

Then you can use this function to change your base_array variable accordingly:

base_array := array_subtract(base_array, temp_array);

---

Using the @Denis's faster solution, and only SQL, we can express a generic function as

CREATE FUNCTION array_subtract(anyarray,anyarray) RETURNS anyarray AS $f$
  SELECT array(
    SELECT unnest($1)
    EXCEPT
    SELECT unnest($2)
  )
$f$ language SQL IMMUTABLE;