SQL的七种连接

book表：

t_book表：

一：inner join  AB共有的。

 select * from book
 inner join t_book
     on book.t_id=t_book.t_id

查询结果：

二：left join  A表的所有,B表没有的用null

select * from book
left join t_book
    on book.t_id=t_book.t_id

输出结果：

三：RIGHT JOIN  B表的所有，A表没有的用Null

 select * from book
 right join t_book
     on book.t_id=t_book.t_id

输出结果：

四：left join where b.id is not null

select * from book
left join t_book
    on book.t_id=t_book.t_id
where t_book.t_id is not null ;

五：right join where a.id is not null

select * from book
right join t_book
    on book.t_id=t_book.t_id
where book.t_id is not null ;

六：full outer join

七：full outer join where b.id is not null

第六和第七MySQL没有这种写法

八：笛卡尔集   两个表相乘。

select * from book,t_book