ALTER TABLE `#__testquestions_results`
  ADD COLUMN `points_before` int unsigned NOT NULL DEFAULT 0 AFTER `percentage`,
  ADD COLUMN `points_after` int unsigned NOT NULL DEFAULT 0 AFTER `points_before`;

UPDATE `#__testquestions_results`
SET `points_before` = `correct_count`,
    `points_after` = `correct_count`
WHERE `points_before` = 0 AND `points_after` = 0;