基于实际项目的SQL学习总结

/*标题：一个项目涉及到的50个Sql语句(整理版)说明：以下五十个语句都按照测试数据进行过测试，最好每次只单独运行一个语句。*/--1.学生表Student(S,Sname,Sage,Ssex) --S 学生编号,Sname 学生姓名,Sage 出生年月,Ssex 学生性别--2.课程表 Course(C,Cname,T) --C --课程编号,Cname 课程名称,T 教师编号--3.教师表 Teacher(T,Tname) --T 教师编号,Tname 教师姓名--4.成绩表 SC(S,C,score) --S 学生编号,C 课程编号,score 分数*/--创建测试数据create table Student(S varchar(10),Sname nvarchar(10),Sage datetime,Ssex nvarchar(10))insert into Student values('01' , N'赵雷' , '1990-01-01' , N'男')insert into Student values('02' , N'钱电' , '1990-12-21' , N'男')insert into Student values('03' , N'孙风' , '1990-05-20' , N'男')insert into Student values('04' , N'李云' , '1990-08-06' , N'男')insert into Student values('05' , N'周梅' , '1991-12-01' , N'女')insert into Student values('06' , N'吴兰' , '1992-03-01' , N'女')insert into Student values('07' , N'郑竹' , '1989-07-01' , N'女')insert into Student values('08' , N'王菊' , '1990-01-20' , N'女')create table Course(C varchar(10),Cname nvarchar(10),T varchar(10))insert into Course values('01' , N'语文' , '02')insert into Course values('02' , N'数学' , '01')insert into Course values('03' , N'英语' , '03')create table Teacher(T varchar(10),Tname nvarchar(10))insert into Teacher values('01' , N'张三')insert into Teacher values('02' , N'李四')insert into Teacher values('03' , N'王五')create table SC(S varchar(10),C varchar(10),score decimal(18,1))insert into SC values('01' , '01' , 80)insert into SC values('01' , '02' , 90)insert into SC values('01' , '03' , 99)insert into SC values('02' , '01' , 70)insert into SC values('02' , '02' , 60)insert into SC values('02' , '03' , 80)insert into SC values('03' , '01' , 80)insert into SC values('03' , '02' , 80)insert into SC values('03' , '03' , 80)insert into SC values('04' , '01' , 50)insert into SC values('04' , '02' , 30)insert into SC values('04' , '03' , 20)insert into SC values('05' , '01' , 76)insert into SC values('05' , '02' , 87)insert into SC values('06' , '01' , 31)insert into SC values('06' , '03' , 34)insert into SC values('07' , '02' , 89)insert into SC values('07' , '03' , 98)go

--1、查询"01"课程比"02"课程成绩高的学生的信息及课程分数--1.1、查询同时存在"01"课程和"02"课程的情况select a.* , b.score [课程'01'的分数],c.score [课程'02'的分数] from Student a , SC b , SC cwhere a.S = b.S and a.S = c.S and b.C = '01' and c.C = '02' and b.score > c.score--1.2、查询同时存在"01"课程和"02"课程的情况和存在"01"课程但可能不存在"02"课程的情况(不存在时显示为null)(以下存在相同内容时不再解释)select a.* , b.score [课程"01"的分数],c.score [课程"02"的分数] from Student aleft join SC b on a.S = b.S and b.C = '01'left join SC c on a.S = c.S and c.C = '02'where b.score > isnull(c.score,0)

--2、查询"01"课程比"02"课程成绩低的学生的信息及课程分数--2.1、查询同时存在"01"课程和"02"课程的情况select a.* , b.score [课程'01'的分数],c.score [课程'02'的分数] from Student a , SC b , SC cwhere a.S = b.S and a.S = c.S and b.C = '01' and c.C = '02' and b.score < c.score--2.2、查询同时存在"01"课程和"02"课程的情况和不存在"01"课程但存在"02"课程的情况select a.* , b.score [课程"01"的分数],c.score [课程"02"的分数] from Student aleft join SC b on a.S = b.S and b.C = '01'left join SC c on a.S = c.S and c.C = '02'where isnull(b.score,0) < c.score

--3、查询平均成绩大于等于60分的同学的学生编号和学生姓名和平均成绩select a.S , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_scorefrom Student a , sc bwhere a.S = b.Sgroup by a.S , a.Snamehaving cast(avg(b.score) as decimal(18,2)) >= 60order by a.S

--4、查询平均成绩小于60分的同学的学生编号和学生姓名和平均成绩--4.1、查询在sc表存在成绩的学生信息的SQL语句。select a.S , a.Sname , cast(avg(b.score) as decimal(18,2)) avg_scorefrom Student a , sc bwhere a.S = b.Sgroup by a.S , a.Snamehaving cast(avg(b.score) as decimal(18,2)) < 60order by a.S--4.2、查询在sc表中不存在成绩的学生信息的SQL语句。select a.S , a.Sname , isnull(cast(avg(b.score) as decimal(18,2)),0) avg_scorefrom Student a left join sc bon a.S = b.Sgroup by a.S , a.Snamehaving isnull(cast(avg(b.score) as decimal(18,2)),0) < 60order by a.S

--5、查询所有同学的学生编号、学生姓名、选课总数、所有课程的总成绩--5.1、查询所有有成绩的SQL。select a.S [学生编号], a.Sname [学生姓名], count(b.C) 选课总数, sum(score) [所有课程的总成绩]from Student a , SC bwhere a.S = b.Sgroup by a.S,a.Snameorder by a.S--5.2、查询所有(包括有成绩和无成绩)的SQL。select a.S [学生编号], a.Sname [学生姓名], count(b.C) 选课总数, sum(score) [所有课程的总成绩]from Student a left join SC bon a.S = b.Sgroup by a.S,a.Snameorder by a.S

--6、查询"李"姓老师的数量--方法1select count(Tname) ["李"姓老师的数量] from Teacher where Tname like N'李%'--方法2select count(Tname) ["李"姓老师的数量] from Teacher where left(Tname,1) = N'李'/*"李"姓老师的数量-----------1*/

--7、查询学过"张三"老师授课的同学的信息select distinct Student.* from Student , SC , Course , Teacherwhere Student.S = SC.S and SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N'张三'order by Student.S

--8、查询没学过"张三"老师授课的同学的信息select m.* from Student m where S not in (select distinct SC.S from SC , Course , Teacher where SC.C = Course.C and Course.T = Teacher.T and Teacher.Tname = N'张三') order by m.S

--9、查询学过编号为"01"并且也学过编号为"02"的课程的同学的信息--方法1select Student.* from Student , SC where Student.S = SC.S and SC.C = '01' and exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = '02') order by Student.S--方法2select Student.* from Student , SC where Student.S = SC.S and SC.C = '02' and exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = '01') order by Student.S--方法3select m.* from Student m where S in( select S from ( select distinct S from SC where C = '01' union all select distinct S from SC where C = '02' ) t group by S having count(1) = 2)order by m.S

--10、查询学过编号为"01"但是没有学过编号为"02"的课程的同学的信息--方法1select Student.* from Student , SC where Student.S = SC.S and SC.C = '01' and not exists (Select 1 from SC SC_2 where SC_2.S = SC.S and SC_2.C = '02') order by Student.S--方法2select Student.* from Student , SC where Student.S = SC.S and SC.C = '01' and Student.S not in (Select SC_2.S from SC SC_2 where SC_2.S = SC.S and SC_2.C = '02') order by Student.S

--11、查询没有学全所有课程的同学的信息--11.1、select Student.*from Student , SCwhere Student.S = SC.Sgroup by Student.S , Student.Sname , Student.Sage , Student.Ssex having count(C) < (select count(C) from Course)--11.2select Student.*from Student left join SCon Student.S = SC.Sgroup by Student.S , Student.Sname , Student.Sage , Student.Ssex having count(C) < (select count(C) from Course)

--12、查询至少有一门课与学号为"01"的同学所学相同的同学的信息select distinct Student.* from Student , SC where Student.S = SC.S and SC.C in (select C from SC where S = '01') and Student.S <> '01'

--13、查询和"01"号的同学学习的课程完全相同的其他同学的信息select Student.* from Student where S in(select distinct SC.S from SC where S <> '01' and SC.C in (select distinct C from SC where S = '01')group by SC.S having count(1) = (select count(1) from SC where S='01'))

--14、查询没学过"张三"老师讲授的任一门课程的学生姓名select student.* from student where student.S not in(select distinct sc.S from sc , course , teacher where sc.C = course.C and course.T = teacher.T and teacher.tname = N'张三')order by student.S

--15、查询两门及其以上不及格课程的同学的学号，姓名及其平均成绩select student.S , student.sname , cast(avg(score) as decimal(18,2)) avg_score from student , scwhere student.S = SC.S and student.S in (select S from SC where score < 60 group by S having count(1) >= 2)group by student.S , student.sname

--16、检索"01"课程分数小于60，按分数降序排列的学生信息select student.* , sc.C , sc.score from student , scwhere student.S = SC.S and sc.score < 60 and sc.C = '01'order by sc.score desc

--17、按平均成绩从高到低显示所有学生的所有课程的成绩以及平均成绩--17.1 SQL 2000 静态select a.S 学生编号 , a.Sname 学生姓名 , max(case c.Cname when N'语文' then b.score else null end) [语文], max(case c.Cname when N'数学' then b.score else null end) [数学], max(case c.Cname when N'英语' then b.score else null end) [英语], cast(avg(b.score) as decimal(18,2)) 平均分from Student aleft join SC b on a.S = b.Sleft join Course c on b.C = c.Cgroup by a.S , a.Snameorder by 平均分 desc--17.2 SQL 2000 动态declare @sql nvarchar(4000)set @sql = 'select a.S ' + N'学生编号' + ' , a.Sname ' + N'学生姓名'select @sql = @sql + ',max(case c.Cname when N'''+Cname+''' then b.score else null end) ['+Cname+']'from (select distinct Cname from Course) as tset @sql = @sql + ' , cast(avg(b.score) as decimal(18,2)) ' + N'平均分' + ' from Student a left join SC b on a.S = b.S left join Course c on b.C = c.Cgroup by a.S , a.Sname order by ' + N'平均分' + ' desc'exec(@sql)--17.3 有关sql 2005的动静态写法参见我的文章《普通行列转换(versio