-- 201_attempts_outcome_backfill.sql (2/6)
-- 기존 attempts 의 is_correct → outcome 매핑 백필.
-- correct: is_correct=true / wrong: is_correct=false. unsure 는 신규 입력에서만 발생.

UPDATE study_question_attempts
SET outcome = CASE WHEN is_correct THEN 'correct' ELSE 'wrong' END
WHERE outcome IS NULL;