内关联和外关联

1. 内链接

select a.*,b.* from a,b where a.aa=b.bb;

等于select a.*,b.* from a inner join b on a.aa=b.bb;

等于select a.*,b.* from a join b on a.aa=b.bb;

2. 外连接

select a.*,b.* from a right join b on a.aa=b.bb;

select a.*,b.* from a left join b on a.aa=b.bb;