Banco de dados do curso do aluno - primeiro familiarizado com a instrução sql (01)

create table student1
( sno char(9) primary key,
  sname char (20) unique,
  ssex char (2),
  sage smallint,
  sdept char(20),
)

create table course1
(cno char(4) primary key,
 cname char(40) not null,
 cpno char(4) references course1(cno),
 ccredit smallint,
)

create table sc1
(sno char(9) references student1(sno),
 cno char(4) references course1(cno),
 grade smallint,
 primary key(sno,cno),
)

alter table student1 add s_entrance date
alter table student1 drop column s_entrance

drop table sc1
drop table course1
drop table student1

create unique index stuname on student(sno)
create unique index coucno on course(cno)
create unique index scno on sc(sno asc,cno desc)

drop index stuname on student
drop index coucno on course
drop index scno on sc

select*
from Student
where Sname like '刘%'

select*
from Student
where Sname like '李_勇%'

select*
from Student
where Sname like '李\_勇%' escape '\'

select Sno,Cno
from SC
where Grade is not null

select Sno,Grade
from SC
where Cno='3'
order by Grade desc --desc(降序)descending order

select*
from Student
where Sdept='cs'
order by Sage asc --asc(升序)ascending order