编辑代码

CREATE DATABASE test;
use test;
CREATE TABLE S (
	SNO char(6) primary key,
    SN char(10) not null,
    SD char(16),
    SB date,
    SEX char(2) default '女',
    check(SEX in('男','女'))
);
CREATE TABLE C (
    CNO char(6) primary key,
    CN char(10),
    PC char(6),
    foreign key (PC) references C(CNO)
);
CREATE TABLE SC (
	SNO char(6) ,
    CNO char(6),
    GRADE DEC(4,1),
    primary key(SNO,CNO),
    foreign key (SNO) references S(SNO),
    foreign key (CNO) references C(CNO),
    check(GRADE between 0 and 100)
);

alter table St add SH char(30);
alter table St add primary key(SNO);
alter table St modify column SN char(12);
alter table St change column Sdept Sdept char(20);
alter table St drop column Ssex;
alter table St drop constraint Sname;
alter table St alter Ssex set default '女';
alter table St alter Ssex drop default '女';
drop table S cascade;

SELECT * FROM S;