sql--仅用来测试blog

Sql代码 
create table people( 
  id int , 
  sex varchar(20), 
  class int 
); 
create table class( 
  id int , 
  classno varchar(20) 
); 
 
insert into people value(1,'g',1), 
                        (2,'b',2), 
                        (3,'g',3); 
insert into class value (1,'one class'), 
                        (2,'two class'); 
select * from people; 
select * from class; 
 
select * from people p,class c where p.class=c.id; 
select * from people p left join  class c on p.class=c.id; 
select * from people p right join  class c on p.class=c.id; 
select * from people p cross join class c;