UPDATE
    scores as sc
SET
    passed = case when(sc.score >= sub.avg)then true
    else
        false
    end
from
    (select 
        subject_code, AVG(score)as avg
    from
        scores
    group by subject_code
    ) as sub
WHERE 
    sc.subject_code = sub.subject_code;
    
UPDATE 
    scores
SET 
    passed = FALSE
WHERE 
    passed IS NULL;