MySQL查询

内连接 

select   a.*,b.* from tablename a inner join tablename b on a.id=b.id

等于

select a.*,b.* from tablename a,tablename b where a.id=b.id

 

左连接

select  a.*,b.* from tablename a left join tablename b on a.id=b.id

 

右连接

select  a.*,b.* from tablename a right join tablename b on a.id=b.id