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  • 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 '',
           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 '',
           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 '',
           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 '',
           enterdate date,
           clazz varchar2(10),
           email varchar2(20)
    );
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  • 原文地址:https://www.cnblogs.com/superdrew/p/8058204.html
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