SQL mapping ids to values in arrays

Question

I have been struggling writing this query. Say, I have mapping table and table with arrays of ids. I want to query for table with arrays of values:

id|value     id_arr            value_arr
--+-----    ---------          ---------
 1|  4      {1, 2}       ->    {4, 5}
 2|  5      {1, 3}             {4, 7}
 3|  7      {1, 2, 3}          {4, 5, 7}

Anyone got idea on this one?

I'm using PostgreSQL, but I think it doesn't change much.

Answer 1

You can unnest the values and reaggregate:

select t2.*,
       (select array_agg(t1.val)
        from unnest(t2.arr) arr_val join
             t1
             on t1.id = arr_val
       ) as arr_ids
from t2 ;

If you want to preserve the original ordering, you can use with ordinality :

select t2.*,
       (select array_agg(t1.val order by n)
        from unnest(t2.arr) with ordinality u(arr_val, n) join
             t1
             on t1.id = arr_val
       ) as arr_ids
from t2 ;

Here is a db<>fiddle.