題目：按各科成績進行排序，並顯示排名
分析：這題目我自己不會做，看答案的 ，哈哈哈哈
sql:
SELECT a.courseid,a.studentid,a.score,COUNT(b.score)+1 AS rank FROM student_score a
LEFT JOIN student_score b ON a.score < b.score AND a.courseid = b.courseid
GROUP BY a.courseid, a.studentid,a.score ORDER BY a.courseid,rank ASC;
運行：
