Union语句 联接

1交叉联接

 --交叉联接
 
 create table toys
 (
   toy_id int identity primary key not null,
   toy varchar(30)
 )
 
 create table boys
 (
   boy_id int not null primary key,
   boy varchar(20)
 )
 insert into toys(toy)values('hula hoop')
 insert into toys(toy)values('balsa glider')
  insert into toys(toy)values('toy soldiers')
   insert into toys(toy)values('harmonica')
    insert into toys(toy)values('baseball cards')
  
 
 
  insert into boys(boy_id, boy)values(1,'Davey')
  insert into boys(boy_id, boy)values(2,'Bobby')
  insert into boys(boy_id, boy)values(3,'Beaver')
  insert into boys(boy_id, boy)values(4,'Richie')

 select t.toy, b.boy from toys t cross join boys b

cross join 返回两张表的每一行相乘的结果。