一、创建表

学生表： 教师表：

二、分步查询

SELECT s.id,s.Sname,t.Tname FROM student s,teacher t where s.t_id = t.id

①：设置实体类

public class Student {
          
   

    private Integer id;
    private String Sname;
    private String sex;
    private Integer age;
    private Integer t_id;
    //这个是重点
    private Teacher teacher;
}

public class Teacher {
          
   
    private Integer id;
    private String Tname;
}

②：查询语句；在studentMapper.xml当中设置分步查询

<select id = "getStudent"  resultMap="StudentTeacher">
    select * from student;
</select>
<resultMap id="StudentTeacher"  type="com.qcby.entity.Student">
    <result property="id" column="id"/>
    <result property="Sname" column="Sname"/>
    <result property="sex" column="sex"/>
    <result property="age" column="age"/>
    <result property="t_id" column="t_id"/>
    <association property="teacher" column="t_id" javaType="com.qcby.entity.Teacher" select="com.qcby.mapper.TeacherMapper.getTeacher"/>
</resultMap>

③配置studentMapper Student getStudent(); ④在TeacherMapper.xml当中设置关于教师的查询

<select id="getTeacher" resultType="com.qcby.entity.Teacher" parameterType="java.lang.Integer">
    select  * from  teacher where id = #{
          
   t_id};    <!-- #{
          
   id}; 可以写任何东西，因为会自动匹配 t_id -->
</select>

⑤配置TeacherMapper Teacher getTeacher(Integer id);

测试：