内链接--取共有部分
select <select_list>
from tableA a
inner join tableB b
on a.key =b.key
ab共有加a的独有（全a）--左链接
select<select_list>
from tableA a
left join tableB b
on a.key=b.key
b独有+ab共有(全b)
select<select_list>
from tableA a
right join tableB b
on a.key=b.key
select<select_list>
frin tableA a
left join tableB b
on a.key =b.key
where b.key is null
select<select_list>
from tableA a
right join tableB b
on a.key=b.key
where a.key is null
select<select_list>
from tableA a
full outer join tableB b
on a.key=b.key
select<select_list>
from tableA a
full outer join tableB b
on a.key=b.key
where a.key is null
or b.key is null
作者：三号小玩家
