SELECT S.SN, SC.C#, SC.GRADE FROM S WHERE S.S#=SC.S#
SELECT S.SN, SC.C#, SC.GRADE FROM SC WHERE S.S#=SC.GRADE
SELECT S.SN, SC.C#, SC.GRADE FROM S, SC WHERE S.S#=SC.S#
SELECT S.SN, SC.C#, SC.GRADE FROM S.SC