UPDATE scores AS sc
SET ranking = sub.ranking
FROM (
    SELECT
        student_code,
        subject_code,
        score,
        RANK() OVER(PARTITION BY subject_code ORDER BY score DESC) AS ranking
    FROM scores
) AS sub
WHERE sc.student_code = sub.student_code
    AND sc .subject_code = sub.subject_code;
    
    SELECT * FROM scores
    
    ORDER BY subject_code,ranking ;