1.left join ==left outer join
2.inner join==join
Select * From A as a Inner Join B as b On a.id=b.pid select * from a,b where a.c=b.c 等价于select * from a inner join b on a.c=b.c；
3.right join
4.full outer join
参考：
https://www.cnblogs.com/reaptomorrow-flydream/p/8145610.html
