UPDATE
    SCORES
SET
    SCORE = 
    CASE
    WHEN
        SCORE + 5 > 100
    THEN
        100
    ELSE
         SCORE + 5
    END
FROM
    STUDENTS
WHERE
    SCORES.STUDENT_CODE = STUDENTS.STUDENT_CODE
AND
    STUDENTS.STUDENT_NAME IN('佐藤 幸平','山田 康介')
;