drop table student;
create table student
(sno int not null unique,
sname varchar(8) not null,
ssex char(2) not null,
sage int ,
sdept varchar(20));
select * from student;
alter table student drop unique(sno);
alter table student modify sno primary key;
alter table student add constraints con_s check(ssex in('F', 'M'));
insert into student values ('0001', 'zhangwen', 'F', 24, 'math');
insert into student values ('0201', 'zhangzi', 'F', 24, 'jsj');
insert into student values ('0002', 'wangjing', 'M', 22, 'math');
insert into student values ('0301', 'lilu', 'M', 23, 'wuli');
insert into student values ('0003', 'wujun', 'M', 24, 'math');
insert into student values ('0202', 'wangli', 'F', 23, 'jsj');
insert into student values ('0203', 'jiangmin', 'M', 23, 'jsj');
insert into student values ('0302', 'lixiang', 'F', 23, 'wuli');
insert into student values ('0303', 'jinmin', 'F', 24, 'wuli');
insert into student values ('0304', 'jinmin', 'F', null, 'wuli');
insert into student values ('0204', 'jinmin', 'F', 22, '');
delete from student where sno = '0204';
update student set sname = 'luyong' where sno = '0304';
insert into student values('0004','meinv','M',22,'math');
insert into student values('0006','beauty','M',21,'math');
----------------------------------------------
drop table course;
create table course(cno int primary key,
cname varchar2(10) not null,
ccredite float(2));
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