Oracle之约束条件1：主键约束

--建立一张用来存储学生信息的表：字段包含学号、姓名、性别，年龄、入学日期、班级，email等信息

--学号是主键
--姓名不能为空
--性别默认值是男
--年龄范围20---80岁
--Email唯一

--主键一个表中只能允许存在一个
drop table student purge;
create table student(
       sno number(6),
       sname varchar2(15),
       age number(2),
       sex   char(2)  default '男',
       enterdate date,
       clazz varchar2(10),
       email varchar2(20),
       constraints PK_STUDENT primary key (sno),--表级别设置主键
       constraints PK_STUDENT1 primary key (email)
);
insert into student values (1,'SuperDrew',21,null,sysdate,'1001','XXXXXX@XXXX.XXXX');
insert into student values (1,'Alia',99,null,sysdate,'1001','XXXXXX@XXXX.XXXX');
insert into student values (1,'Bob',25,null,sysdate,'1001','XXXXXX@XXXX.XXXX');
insert into student values (1,null,11,null,sysdate,'1001','XXXXXX@XXXX.XXXX');

--第二种方式设定主键  
drop table student purge;
create table student(
       sno number(6) primary key ,--列级别设置主键 简化的操作
       sname varchar2(15),
       age number(2),
       sex   char(2)  default '男',
       enterdate date,
       clazz varchar2(10),
       email varchar2(20)
);


--组合式主键
--组合主键 只有指定的主键的列 数据都一样 才不能写入表中
drop table student purge;
create table student(
       sno number(6),
       sname varchar2(15),
       age number(2),
       sex   char(2)  default '男',
       enterdate date,
       clazz varchar2(10),
       email varchar2(20),
       constraints PK_STUDENT primary key (sno,sname)--表级别设定主键
);
insert into student values (1,'KING',18,null,sysdate,'1002','XXXXXX@XXXX.XXXX');
insert into student values (3,'Geny',18,null,sysdate,'1002','XXXXXX@XXXX.XXXX');
insert into student values (2,'Tidy',18,null,sysdate,'1002','XXXXXX@XXXX.XXXX');


select * from student;


--联合主键只能通过表级别设定，列级别是不能设定联合主键
drop table student purge;
create table student(
       sno number(6) primary key,
       sname varchar2(15) primary key,
       age number(2),
       sex   char(2)  default '男',
       enterdate date,
       clazz varchar2(10),
       email varchar2(20)
);