请教个问题，关于mybatis多表查询
如
class A{
private String Aid;
private String Aname;
getter..setter..
}
class B{
private String Bid;
private String Bname;
private A a;
getter..setter..
}
查询的sql是select a.id,a.name,b.id,b.name from a,b where a.id = b.id
请指教
这个具体怎么写，实了很多种方法，都没有办法成功
有个例子：
[code="xml"]
select a.id,a.name,b.id,b.name from a,b where a.id = b.id
[/code]
参考
[url]http://www.ibm.com/developerworks/cn/opensource/os-cn-ibatis/[/url]
曾经的JAVA天堂，
现在有点失望了。
select a.id,a.name,b.id,b.name from a,b where a.id = b.id
这不是要在B中增加原本A的属性，
增加一堆多余的代码？
[code="java"]
select
a.id as comtid,
a.content as comtContent ,
b.id as personID,
b.name as personName
from comment a
LEFT JOIN person b on a.personid=b.id
where a.id=#{id}
[/code]
[code="xml"]
select
a.id as comtid,
a.content as comtContent ,
b.id as personID,
b.name as personName
from comment a
LEFT JOIN person b on a.personid=b.id
where a.id=#{id}
[/code]