查询语句
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') as a,(selects#,score
  from SC where C#='002') as 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 join SC on Student.S#=SC.S#
  group by Student.S#,Sname
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“张三”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# andTeacher.Tname='张三')
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# andSC_2.C#='002')
7、查询学过“张三”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='张三' group by S# having count(SC.C#)=(select count(C#) from Course,Teacher  whereTeacher.T#=Course.T# and Tname='张三'))
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') as score2
  from Student,SC where Student.S#=SC.S# and C#='001') S_2 where score2<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# andscore>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 whereS#='001')
13、把“SC”表中“张三”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='张三'
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 whereS#='1002')
group by S# having count(*)=(select count(*) from SC whereS#='1002')
15、删除学习“张三”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='张三'
16、向SC表中插入一些记录，这些记录要求符合以下条件：
学号是没有上过编号“002”课程的同学学号
sql语句查询不包含
课程号是002
成绩是002号课的平均成绩；
Insert into SC
values（select S# from Student where S# not in (Select S# from SC where C#='002'),'002',
(Select avg(score)
  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
  where R.C# = IR.C# group by IR.C# )
19、按各科平均成绩从低到高和及格率的百分数从高到低顺序
SELECT t.C# as 课程号,max(course.Cname) as课程名,isnull(AVG(score),0) as 平均成绩,100 * SUM(case when isnull(score,0)>=60 then 1 else 0 end)/count(*) as 及格百分数
from SC T,Course
where t.C#=course.C#
group by t.C#
order by 100 * SUM(case when  isnull(score,0)>=60 then 1 else 0 end)/count(*) DESC
20、查询如下课程平均成绩和及格率的百分数(用"1行"显示): 企业管理（001），马克思（002），OO&UML （003），数据库（004）
SELECT SUM(CASE WHEN C# ='001' THEN score ELSE 0END)/SUM(CASE C# WHEN '001' THEN 1 ELSE 0 END) AS 企业管理平均分
        ,100 * SUM(CASE WHEN C# = '001' ANDscore >= 60 THEN 1 ELSE 0 END)/SUM(CASE WHEN C# = '001' THEN 1 ELSE 0 END)AS 企业管理及格百分数

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