建立三個表:Student(學生信息表),Course(課程表),SC(學生選課表)
create table Student(Sno char(9)PRIMARY KEY,
Sname char(20)UNIQUE,
Ssex char(2),
Sage SMALLINT,
Sdept char(20));
create table Course(Cno char(4)PRIMARY KEY,
Cname char(40) not null,
Cpno char(4),
Ccredit SMALLINT,
FOREIGN KEY (Cpno)REFERENCES Course(Cno));
create table SC(Sno char(9),
Cno char(4),
Grade SMALLINT,
PRIMARY KEY(Sno,Cno),
FOREIGN KEY (Sno)REFERENCES Student(Sno),
FOREIGN KEY (Cno)REFERENCES Course(Cno),);
存入信息:
insert into Student () values ();
insert into Course () values ();
insert into SC () values ();
向student表添加記錄(10條記錄添加方式一樣)
insert into Student (Sno,Sname,Ssex,Sage,Sdept) values
('201616041','張三','男',20,'CS');
向course表添加記錄(10條記錄添加方式一樣)
insert into Course (Cno,Cname,Cpno,Ccredit) Values
('1102','數學',NULL,2);
向sc表添加記錄(10條記錄添加方式一樣)
insert into SC(Sno,Cno,Grade) values
('201616040','1101',54);
對Student的執行增刪改操作(三條語句分別爲插入,修改,刪除)
insert into Student (Sno,Sname,Ssex,Sage,Sdept) values
('201616055','宋十五','男',22,'CS');
update Student set Sage = 50 where Sno='201616055';
delete from Student where Sno='201616055';
對Course的執行增刪改操作(三條語句分別爲修改,插入,刪除)
update Course set Ccredit = 10 where Cno='1101';
insert into Course(Cno,Cname,Cpno,Ccredit) values
('1111','政治',null,4);
delete from Course where Cno='1109';
delete from Course where Cno='1103';
對SC的執行增刪改操作(三條語句分別爲插入,修改,刪除)
insert into SC(Sno,Cno,Grade) values
('201616058','1101',22);
update SC set Cno=1106 where Sno='201616058';
delete from SC where Sno='201616040';
對Student表做修改表結構練習(依次是增加列,修改列的屬性,修改列的名稱,刪除列)
alter table Student add CardID varchar(16);
alter table Student alter column CardID varchar(400) ;
EXEC sp_rename 'Student.CardID','CardIDTest';
alter table Student drop column CardIDTest;
select * from Student where Sdept='CS'; //查詢計算機系學生的信息;
select count(*) from Student; //查詢全體學生的人數;
select Ssex, count(Ssex) 人數 from Student group by Ssex; //查詢全體男生人數和女生人數;
//查詢每個系中的男生人數並按人數的降序排列;
select Sdept,Ssex,count(Sdept) 人數
from Student
group by Ssex ,Sdept
having Ssex='男'
order by count(Sdept);
select * from Student Where Sname LIKE '%十%'; //查詢名字中帶“十”的學生信息;
//求被選修的各門課程的平均成績和選修該課程的人數;
select Cno 課程號,count(Sno) 人數,AVG(Grade) 平均成績
from SC
where Grade is not null
group by Cno;
//查找選修課程超過2門且成績都在80分以上的學生的學號。由於最初使的表不存在這樣的學生,於是我在SC表中又添加了一行201616044學生的信息 insert into SC values ('201616044','1108',98);
select Sno
from sc
where Grade>80
group by sno
having count(Sno)>=2;
單表查詢(針對上述三個表):