day02

SELECT DISTINCT student.* FROM student RIGHT JOIN sc ON student.SId = sc.SId

SELECT
    t1.SId,
    t1.Sname,
    t2.count,
    t2.sum 
FROM
    student t1
    LEFT JOIN ( SELECT SId, count( CId ) count, SUM( score ) sum FROM sc GROUP BY SId ) t2 ON t1.SId = t2.SId