50个常用sql语句

re S#=''001'');
13、把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩;
    update SC set score=(select avg(SC_2.score)
    from SC SC_2
    where SC_2.C#=SC.C# ) from Course,Teacher where Course.C#=SC.C# and Course.T#=Teacher.T# and Teacher.Tname=''叶平'');
14、查询和“1002”号的同学学习的课程完全相同的其他同学学号和姓名;
    select S# from SC where C# in (select C# from SC where S#=''1002'')
    group by S# having count(*)=(select count(*) from SC where S#=''1002'');
15、删除学习“叶平”老师课的SC表记录;
    Delect SC
    from course ,Teacher 
    where Course.C#=SC.C# and Course.T#= Teacher.T# and Tname=''叶平'';
16、向SC表中插入一些记录，这些记录要求符合以下条件：没有上过编号“003”课程的同学学号、2、
    号课的平均成绩;
    Insert SC select S#,''002'',(Select avg(score)
    from SC where C#=''002'') from Student where S# not in (Select S# from SC where C#=''002'');
17、按平均成绩从高到低显示所有学生的“数据库”、“企业管理”、“英语”三门的课程成绩，按如下形式显示： 学生ID,,数据库,企业管理,英语,有效课程数,有效平均分
    SELECT S# as 学生ID
        ,(SELECT score FROM SC WHERE SC.S#=t.S# AND C#=''004'') AS 数据库
        ,(SELECT score FROM SC WHERE SC.S#=t.S# AND C#=''001'') AS 企业管理
        ,(SELECT score FROM SC WHERE SC.S#=t.S# AND C#=''006'') AS 英语
        ,COUNT(*) AS 有效课程数, AVG(t.score) AS 平均成绩
    FROM SC AS t
    GROUP BY S#
    ORDER BY avg(t.score) 
18、查询各科成绩最高和最低的分：以如下形式显示：课程ID，最高分，最低分
    SELECT L.C# As 课程ID,L.score AS 最高分,R.score AS 最低分
    FROM SC L ,SC AS R
    WHERE L.C# = R.C# and
        L.score = (SELECT MAX(IL.score)
                      FROM SC AS IL,Student AS IM
                      WHERE L.C# = IL.C# and IM.S#=IL.S#
                      GROUP BY IL.C#)
        AND
        R.Score = (SELECT MIN(IR.score)
                      FROM SC AS IR
                  &