数据双项表的建立

select *from books;
insert into books values('英语','中国出版社',900);
insert into books values('德语','德国出版社',500);
insert into books values('英语','英国出版社',700)；
select *from books where name like'%英语%';


create table room(
       RoomID number(5) constraint room_pk primary key,
       RoomName varchar2(255)
       );
create table student(
　　　StudentID number(5) constraint student_pk primary key,
　　　StudentName varchar2(255),
      RoomID number(5),
      foreign key (RoomId) references room(RoomID)
　　　);

insert into room values(1,'教室1');
insert into room values(2,'教室2');
insert into room values(3,'教室3');
insert into student values(1,'学生1',1);insert into student values(2,'学生2',2);
insert into student values(3,'学生3',3);

select * from room ;　
select * from student;　　

drop table student;
drop table room ;

表的内链接：两表里面的数据完全一样
select StudentId 编号,StudentName 姓名,RoomId 教室 from Student;
select s.StudentId 编号,s.StudentName 姓名,r.RoomName 教室 from Student s,Room r where s.Studentid=r.roomid;

左外查询:以左边为主，如果右表没有匹配则为空替代 select s.StudentId 编号,s.StudentName 姓名,r.RoomName 教室 from Student s,Room r where s.Studentid=r.roomid(+);

右连接查询：以右边为主，如果左表没有匹配则为空替代select s.StudentId 编号,s.StudentName 姓名,r.RoomName 教室 from Student s,Room r where s.Studentid(+)=r.roomid;


子查询
select *from Student where StudentId in(select RoomId from Room);