面试题--比较简单就是不会

SELECT st.stunum,st.stuname,c.classname,COUNT(sc.kcbh)
FROM class c,score sc,student st WHERE c.classid=st.classid AND st.stunum=sc.stunum GROUP BY sc.stunum;

SELECT st.stunum,st.stuname,c.classname, AVG(sc.score),SUM(sc.score)
FROM class c,score sc,student st WHERE c.classid=st.classid AND st.stunum=sc.stunum GROUP BY sc.stunum ORDER BY COUNT(sc.kcbh) DESC;

SELECT st.stunum,st.stuname,c.classname, MAX(sc.score) as 最大成绩
FROM class c,score sc,student st WHERE c.classid=st.classid AND st.stunum=sc.stunum GROUP BY c.classid；

自己十几分钟造了些数据，回忆写了一下，问题不大