update scores as s
   set passed=CASE WHEN s.score>=avgtbl.avg_score THEN TRUE ELSE FALSE END
--   set passed=TRUE
  from (select test_code, subject_code, avg(score) as avg_score from scores group by test_code, subject_code) as avgtbl
  where s.test_code=avgtbl.test_code
    and s.subject_code=avgtbl.subject_code
;