Internal connection query and external connection

Internal connection

select * from a join b on  Conditions 

External connection

The left outer join （ Zuo quanyao , Intersect to , No right ）

left outer join

Right connection （ Just right , Add and ）

cright outer join

Full outer join （ Don't intersect ）

full outer join

oracle There are full join But in the mysql Inside full join Support is not good , We can use union To achieve the goal