SQL 练习7

• 查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩(没成绩的显示为 null )

SELECT Student.SId,sname,t.选课总数,t.总成绩 from Student LEFT JOIN (SELECT sid,COUNT(cid) 选课总数 ,SUM(score) 总成绩 from SC GROUP BY SId ) as t ON Student.SId = t.sid