三道研究生SQL考试大题，请教！

没学过关系代数,我去考最多只能得一半分了.

1.2) select * from student where sno not in (select sno from sc where cno = 'C03')

2.1) select sname, sdept
     from   student
     where  sno not in
            (
            select sno
            from sc
            where cno = 'c001'
             )

2.2)    select    *
        from      SC a join SC b
                  on a.sno = b.sno
        where      = 'c001' and
                   = 'c002' and
                  a.grade > b.grade

2.3)
        select     *
        from       student
        where      sdept = 'd001' and                              -- d001 = 经济系
                   sno in (select sno from sc where grade < 50)    -- 50   = 及格

        

1 1）select 分数 from course where "课程号"=( select 课程号 from SC where "学号"=( select 学号 from student where "姓名"='李明' ) )
2）select * from student where "学号" in ( select 学号 from SC where "课程号"<>'co3' )

还在初级学习阶段