MyBatis怎么只发送一条SQL查询两张表

MyBatis只发送一条SQL查询两张表
一个效率问题，怎么让MyBatis只发送一条SQL语句来查询两个有主外键关系的表

之前写的参考一下

 <resultMap id="userResultMap2" type="User">
<id property="id" column="usrid"/>
<result property="name" column="name"/>
<result property="password" column="password"/>
<result property="sex" column="sex"/>
<result property="birthday" column="birthday"/>
<!-- 关联Group -->
<association property="group" column="gid" javaType="Group">
<id property="id" column="gid"/>
<result property="name" column="gname"/>
</association>

 <!-- 两张表 多对一关联方式查询    -->
<select id="selectUserJoinGroupByUserId" parameterType="Long" resultMap="userResultMap2">
select u.id as usrid,u.name as name,
u.birthday as birthday,
u.sex as sex,u.password as password,
u.gid as gid,
g.name as gname
from SC_USER u join SC_GROUP g on u.gid=g.id 
where u.id=#{id}
</select>

不知道你所要的主外关联是一对一，还是一对多。一对一用association，一对多用conllect