mysql查询选了课的同学的sid和其平均分

Question

mysql中查询选了课的同学的sid及其平均分要怎样写？第九题我写的select sc.sid，avg（score) from student,course,sc where sc.cid is not null 查询后的结果只显示出s1的平均值

Answer 1

SELECT SID, AVG(SCORE) as AVG_SCORE FROM SC_XXX GROUP by SID;