Why not use the native functions [0] of the DB? Presumably they're going to be faster. For example, computing the median of a table `nums` with columns `id` and `num` can be done like this:

    WITH ordered_nums AS (
      SELECT num, ROW_NUMBER() OVER (ORDER BY num) as rn,
             COUNT(*) OVER() as total
      FROM nums
    )
    SELECT AVG(num) as median
    FROM ordered_nums
    WHERE rn IN (
      (total + 1) / 2,
      (total + 2) / 2
    );