Oracle如何给数据库添加约束过程解析

create table stu01(

   sid varchar (100),

   sname varchar2(100)

   --constraint PK_stu01_sid primary key (sid)

  )

  --添加约束(主键)

   alter table stu01 add constraint PK_stu01_sid primary key (sid)  ---添加主键约束

   alter table stu01 drop constraint PK_stu01_sid          ---删除主键约束

create table stu02(

   sid varchar2(100),

   sname varchar2(100),

   constraint PK_stu02_sid primary key (sid),

   constraint UK_stu02_sname unique (sname)

  )

create table stu03(

   sid varchar2(100),

   sname varchar2(100) not null ,

   constraint PK_stu03_sid primary key (sid),

   constraint UK_stu03_sname unique (sname)

  )

create table stu04(

   sid varchar2(100),

   sname varchar2(100) not null ,

   constraint PK_stu04_sid primary key (sid),

   constraint UK_stu04_sname unique (sname)

  )

  --创建课程表

  create table course01(

   cid varchar2(100),

   cname varchar2(100) not null ,

   constraint PK_course01_cid primary key (cid),

   constraint UK_course01_cname unique (cname)

  )

  --最后添加成绩表，外键约束课程表和学生表

   create table mark02(

   sid varchar2(100),

   cid varchar2(100),

   mark number,

   constraint PK_mark02_sidAndcid primary key (sid,cid),

   constraint FK_mark02_sid foreign key (sid) references stu04(sid),

   constraint FK_mark02_cid foreign key (cid) references course01(cid),

   constraint UK_mark02_mark unique (mark)

   )

  --删除外键约束

  alter table mark01 drop constraint FK_mark02_sid

   alter table mark01 drop constraint FK_mark02_cid