UPDATE
 total_scores
SET
 passed = (SELECT
   CASE
    WHEN avg <= total_score THEN "TRUE"
    WHEN total_score < avg THEN "FALSE"
   END AS passed
  FROM (
   SELECT
    s.student_name AS name,
    ts.total_score AS total_score,
    ROUND(AVG(total_score) OVER(), 2) AS avg
   FROM
    students AS s
   INNER JOIN
    total_scores AS ts ON ts.student_code = s.student_code
  )
 );