使用SQL语句创建数据表

写法一

create table student (sno char(10) primary key,sname varchar(20) not null,ssex char(2),sage smallint,sdept varchar(20),sid char(18) unique)

写法二

create table student(sno char(10),sname varchar(20) not null,ssex char(2),sage smallint,sdept varchar(20),sid char(18),primary key(sno),unique(sid))

写法三

create table student(sno char(10)constraint pk_student_sno primary key,sname varchar(20) not null,ssex char(2),sage smallint,sdept varchar(20),sid char(18) constraint uq_student_sid unique)

写法四

create table student(sno char(10),sname varchar(20) not null,ssex char(2),sage smallint,sdept varchar(20),sid char(18),constraint pk_student_sno primary key(sno),constraint uq_student_sid unique(sid))

写法一

create table course(cno char(4) primary key,cname varchar(40),cpno char(4) foreign key references course(cno),ccredit smallint default 2)

写法二

create table course(cno char(4) primary key,cname varchar(40),cpno char(4),ccredit smallint default 2,foreign key(cpno) references course(cno))

cpno是外码 被参照表是course 被参照表是cno

create table sc(sno char(10),cno char(4),grade smallint check(grade>=0 and grade <=100),primary key(sno,cno),foreign key(sno) references student(sno),foreign key(cno) references course(cno))

create table student(sno char(10) primary key,sname varchar(20) unique,ssex char(2) check(ssex in('男','女')),sage smallint not null,sdept varchar(20),check(ssex='女' or sage>=18))