哈工大软件学院数据库实验1

前言

这个实验很简单，我先讲下大致步骤，然后再解释详细点，再附上实验解答

实验内容

这次实验就是说白了，把外部的txt文件通过sqlite等软件导入到一个数据库里面去,这个数据库就是db3后缀的那个文件
然后不是导入进去了吗？导入进去之后就对数据库里面的数据进行一系列的操作，这就达到了实验的目的

实验难点

.初学者不会使用软件，不知道该怎么操作
.不理解相关信息含义，无法写出有质量的代码

相关难点剖析：（利用sqlite）
创建数据库用 .open seen.db3 //seen.db3是自己改的
创建表用create table(…这里面输入各种键值，用来接数据);
.separator “,” 这个里面的逗号是定义txt文件里面的那个分隔符，利用这个分隔符读取文件
关于导入导出的技巧：

1.txt文件千万不能有多余的空格

2.导入时txt文件里面的分割符要和导入的相一致

3.import语句不要分号

4.导入的时候是会重复导入的，前面导入的后面还会有

5.字符串存储相当严格，连空格都会存储进去

实验解答

我看了几年的实验，似乎都是那50道题，认真学习的同学会发现这些都在PPT上能够找到，如果不认真的就上网找吧，但愿你们能够找到这里来，给我博客增添点人气~~~
所以我就直接附上那50道题的代码了，每个都是经过我测试好的。如果其中有问题就找我来问吧，我肯定会帮助你解决的

    11,select sID,sName,GPA from Student where GPA>3.6;

    12,select sID,sName from Student where GPA>3.6;

    13,select sName,cName from Student,Apply where Student.sID = Apply.sID;

    14,select distinct sName,cName from Student,Apply where Student.sID = Apply.sID;
(从上条我们就可以看出，去除重复元组是有多强)

    15,select sName,GPA,decision from Student,Apply where Student.sID=Apply.sID and cName='Stanford' and major='CS' and sizeHS<1000;

    16,select distinct College.cName from College,Apply where College.cName=Apply.cName and major='CS' and enrollment>20000;

    17,select sName,College.cName,GPA,state,enrollment from Apply,Student,College where Apply.sID = Student.sID and Apply.cName = College.cName order by GPA desc;

    在满足上述条件下想让次要条件按enrollment降序就可以在后面加一句enrollment desc;

    18,参照17附加   

    19,select sID,major from Apply where major like '%bio%';

    20,select * from College,Student;

    21，...略

    22,select s1.sName,s2.sName from Student s1,Student s2 where s1.sID!=s2.sID and s1.GPA=s2.GPA;(去除重复元素似乎不管用) ----------有点问题

    22，23 同

    24，select cName from College union all select sName from Student;(含重复)

        不含重复版本：
       select distinct cName from College union all select distinct sName from Student;

    25,select distinct cName as name from College union all select distinct sName as name from Student order by name;

    26,25已经完成

    27，select sID from Apply where major=='CS' intersect select sID from Apply where major = 'EE'; 

    28,select sID from Apply where major=='CS' except select sID from Apply where major = 'EE'; 

    29,select sName,sID from Student where sID in (select sID from Apply where major='CS');

    30,select distinct sName from Student,Apply where Student.sID= Apply.sID and major='CS';

    或者：select distinct sName from Student where sID in(select sID from Apply where major='CS');

    31,select distinct sID from Apply where sID in (select sID from Apply where major = 'CS') and sID not in (select sID from Apply where major = 'EE');

    32,select cName from College s1 where not exists (select * from College s2 where s1.enrollment<s2.enrollment);

    33,select distinct sName,GPA from Student s1 where not exists (select * from Student s2 where s1.GPA<s2.GPA);

    33,select distinct sName,GPA from Student s1 where not exists (select * from Student s2 where s1.GPA<s2.GPA) ;

    34,..

    35,select sName major from Student,Apply where Student.sID=Apply.sID;

    36，select sName,GPA from Student natural join Apply where sizeHS<1000 and cName='Stanford' and major='CS';

        select sName,GPA from Student join Apply using (sID) where sizeHS<1000 and cName='Stanford' and major='CS';

        select sName,GPA from Student join Apply where Student.sID= Apply.sID and sizeHS<1000 and cName='Stanford' and major='CS';

    37,select * from Student natural join Apply natural join College;

    38,

    39,select avg(GPA) from Student ;

    40,select min(GPA) from Student natural join Apply where major='cs';   //聚集查询

    //   select distinct s1.GPA from Student s1 natural join Apply where not exists (select * from Student s2 where s1.GPA>s2.GPA ) and major='CS';

    41，select avg(GPA) from Student natural join Apply where major='CS';

    42,select count(*) from College where enrollment>15000;

    43,select count(*) from Apply where cName='Cornell' and sID in (select distinct sID from Apply); //这个有问题,牛逼牛逼

    44，select CS.avgGPA-NonCS.avgGPA from (select avg(GPA) as avgGPA from Student natural join Apply where major='CS') as CS,(select avg(GPA) as avgGPA from Student where sID not in(select sID from Apply where major='CS')) as NonCS;

    45,select cName,count(*) from Apply group by cName;

    46,select state,sum(enrollment) from College group by state;

    47,select cName,major,max(GPA),min(GPA) from Student natural join Apply group by cName,major;   //group by 可以循环使用

    48,select sID,sName,count(*) from Apply natural join Student group by Apply.sID;

    50,select cName from Apply group by cName having count(*)<5;