Oracle创建主键

Oracle创建主键创建主键⽅式
1.⼀个表的主键是唯⼀标识，不能有重复，不允许为空。

2.⼀个表的主键可以由⼀个字段或多个字段共同组成。

-- 列级，表级建⽴主键
1.create table constraint_test
( name_id number not null constraint cons_name_id primary key,
old number )
2.create table constraint_test
( name_id number primary key,
old number )
drop table constraint_test;
3.create table constraint_test
(
name_id number not null,
old number ,
constraint cons_name_id primary key ( name_id )
);
drop table constraint_test;
4.create table constraint_test
(
name_id number not null,
old number
);
alter table constraint_test add constraint cons_name_id primary key ( name_id );
外键
drop table course ;
drop table students ;
create table students
(code number ,
name varchar2(10),
country varchar2(30)
);
alter table students add constraint pk_st_cod primary key ( code);
insert into students values(0001,'zhangsan','shanghai');
insert into students values(0002,'lisi','beijing');
insert into students values(0003,'wangwu','guangzhou');
create table course
(id number,
code number,
name varchar2(10),
subject varchar2(30)
);
alter table course add constraint pk_co_id primary key ( id);
alter table course add constraint fk_co_st foreign key ( code) references students(code);
alter table students add foreign key pk_co_id on id;
inser into course(id,code,name,subject) values(1,001,'zhangsan','yuwen');
inser into course(id,code,name,subject) values(2,001,'zhangsan','shuxue');
总结：如果要删除有外键的表，必须删除关联表数据。