select c_classid,c_courseid,vag(c_score) group by c_courseid,c_classid
打错了,用 select c_classid,c_courseid,avg(c_score) from t_score group by c_courseid,c_classid
select c_classid,c_courseid,round(avg(c_score),1) from t_score group by c_courseid,c_classid order by c_classid,C_courseid
这个是对的 select a.c_name,b.c_name,c.c_score from t_class a,t_course b, (select c_classid,c_courseid,round(avg(c_score),1) as c_score from t_score group by c_courseid,c_classid order by c_classid,C_courseid) c where a.c_id=c.c_classid and b.c_id=c.c_courseid;
select c_classid,c_courseid,avg(c_score) from t_score group by c_courseid,c_classid
select a.c_name,b.c_name,c.c_score
from t_class a,t_course b,
(select c_classid,c_courseid,round(avg(c_score),1) as c_score from t_score group by c_courseid,c_classid
order by c_classid,C_courseid) c
where a.c_id=c.c_classid and b.c_id=c.c_courseid;
以课程为列
而且课程数由t_course动态确定