题解 | #最差是第几名(一)#

case when

SELECT grade ,CASE grade WHEN 'A' THEN(SELECT SUM(number)
                                       FROM class_grade WHERE grade <='A')
                         WHEN 'B' THEN(SELECT SUM(number)
                                       FROM class_grade WHERE grade <='B')
                         WHEN 'C' THEN(SELECT SUM(number)
                                       FROM class_grade WHERE grade <='C')
                         WHEN 'D' THEN(SELECT SUM(number)
                                       FROM class_grade WHERE grade <='D')
                         ELSE (SELECT SUM(number) FROM class_grade)
                         END AS t_cnt
FROM class_grade
ORDER BY grade ASC;