50个常用sql语句
    Student(S#,Sname,Sage,Ssex) 学生表
    Course(C#,Cname,T#) 课程表
    SC(S#,C#,score) 成绩表
    Teacher(T#,Tname) 教师表
    问题：
    1、查询“001”课程比“002”课程成绩高的所有学生的学号;
    select a.S# from (select s#,score from SC where C#='001') a,(select s#,score
    from SC where C#='002') b
    where a.score>b.score and a.s#=b.s#;
    2、查询平均成绩大于60分的同学的学号和平均成绩;
    select S#,avg(score)
    from sc
    group by S# having avg(score) >60;
    3、查询所有同学的学号、姓名、选课数、总成绩;
    select Student.S#,Student.Sname,count(SC.C#),sum(score)
    from Student left Outer join SC on Student.S#=SC.S#
    group by Student.S#,Snamesql统计每个系的学生人数
    4、查询姓“李”的老师的个数;
    select count(distinct(Tname))
    from Teacher
    where Tname like '李%';
    5、查询没学过“叶平”老师课的同学的学号、姓名;
    select Student.S#,Student.Sname
    from Student
    where S# not in (select distinct( SC.S#) from SC,Course,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname='叶平');
    6、查询学过“001”并且也学过编号“002”课程的同学的学号、姓名;
    select Student.S#,Student.Sname from Student,SC where Student.S#=SC.S# and SC.C#='001'and exists( Select * from SC as SC_2 where SC_2.S#=SC.S# and SC_2.C#='002');
    7、查询学过“叶平”老师所教的所有课的同学的学号、姓名;
    select S#,Sname
    from Student
    where S# in (select S# from SC ,Course ,Teacher where SC.C#=Course.C# and Teacher.T#=Course.T# and Teacher.Tname='叶平' group by S# having count(SC.C#)=(select count(C#) from Course,Teacher where Teacher.T#=Course.T# and Tname='叶平'));
    8、查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名;
    Select S#,Sname from (select Student.S#,Student.Sname,score ,(select score from SC SC_2 where SC_2.S#=Student.S# and SC_2.C#='002') score2
    from Student,SC where Student.S#=SC.S# and C#='001') S_2 where score2 <score;< p=""></score;<>
    9、查询所有课程成绩小于60分的同学的学号、姓名;
    select S#,Sname
    from Student
    where S# not in (select Student.S# from Student,SC where S.S#=SC.S# and score>60);
    10、查询没有学全所有课的同学的学号、姓名;
    select Student.S#,Student.Sname
    from Student,SC
    where Student.S#=SC.S# group by Student.S#,Student.Sname having count(C#) <(select count(C#) from Course);
    11、查询至少有一门课与学号为“1001”的同学所学相同的同学的学号和姓名;
    select S#,Sname from Student,SC where Student.S#=SC.S# and C# in select C# from SC where S#='1001';
    12、查询至少学过学号为“001”同学所有一门课的其他同学学号和姓名;
    select distinct SC.S#,Sname
    from Student,SC
    where Student.S#=SC.S# and C# in (select C# from SC where 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

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