Mybatis 子查询

子查询：

同表中子查询直接在statement中写，和sql格式一样；

不同表间的子查询通过resultMap来实现：

<resultMap type = "Book" id = "BookAndReader" autoMapping = "true">
    <id colume = "id" property = "id"/>
    <association property = "reader" javaType = "Reader" autoMapping = "true" select = "queryReaderById" column = "user_id">
        <!--select进行子查询声明，其参数为子查询语句ID-->
        <!--column为子查询参数，即从pojo类传过来的#{id}-->
    </association>
</resultMap>
<select id = "queryReaderAll" resultMap = "BookAndReader">
    select * from tb_order where order_number = #{number}
</select>
<select id = "queryReaderById" resultType = "Reader">
    <!--这里是子查询实体-->
    select * from tb_user where id = #{id}
</select>

这里应该是主查询先执行