create table teacher(
    id int not null,
    name varchar(30) default null,
    primary key (id)
);

insert into teacher (id, name) values (1, '蔡老師');

create table student(
    id int not null ,
    name varchar(30) default null,
    tid int default null,
    constraint fk_tid foreign key (tid) references teacher(id)
);

insert into student(id, name, tid) VALUES (1, '小名', 1);
insert into student(id, name, tid) VALUES (2, '小紅', 1);
insert into student(id, name, tid) VALUES (3, '小亮', 1);
insert into student(id, name, tid) VALUES (4, '小蘭', 1);
insert into student(id, name, tid) VALUES (5, '笑笑', 1);

//查詢所有的學(xué)生信息以及對(duì)應(yīng)的老師的信息
List<Student> queryStudentAndTeacher();

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;

    //學(xué)生需要關(guān)聯(lián)一個(gè)老師
    private Teacher teacher;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;
}

<!--思路：
	1.查詢所有的學(xué)生
	2.根據(jù)查詢出來(lái)的學(xué)生的tid尋找對(duì)應(yīng)的老師  尋找對(duì)應(yīng)的老師，子查詢
-->
<resultMap id="rStuAndTea" type="student">
    <result property="id" column="id"/>
    <result property="name" column="name"/>
    <!-- 復(fù)雜的屬性我們需要單獨(dú)處理  
							指定屬性的類型
		 對(duì)象使用association  javaType
		 集合使用collection   ofType
	-->
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacher"/>
</resultMap>
<select id="queryStudentAndTeacher" resultMap="rStuAndTea">
    select * from student
</select>
<select id="getTeacher" resultType="teacher">
    select * from teacher where id = #{id}
</select>

<!--方式二  按照結(jié)果嵌套處理-->
<resultMap id="rStuAndTea2" type="student">
    <result property="id" column="sid"/>
    <result property="name" column="sname"/>
    <association property="teacher" javaType="Teacher">
        <result property="name" column="tname"/>
    </association>
</resultMap>
<select id="queryStudentAndTeacher2" resultMap="rStuAndTea2">
    select s.id sid, s.name sname, t.name tname
    from student s, teacher t
    where s.tid = t.id
</select>

//查詢指定老師的信息及其所有的學(xué)生
Teacher queryTeaAndStu(@Param("tid") int id);

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Teacher {
    private int id;
    private String name;

    //一個(gè)老師擁有多個(gè)學(xué)生
    private List<Student> students;
}

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private int id;
    private String name;
    private int tid;
}

<!--按照結(jié)果嵌套查詢-->
<resultMap id="rTeaAndStu" type="teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>
    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <result property="tid" column="tid"/>
    </collection>
</resultMap>
<select id="queryTeaAndStu" resultMap="rTeaAndStu">
    select s.id sid, s.name sname, t.name tname, t.id tid
    from student s, teacher t
    where s.tid = t.id and t.id = #{tid}
</select>

<!--按照查詢嵌套處理-->
<select id="queryTeaAndStu2" resultMap="rTeaAndStu2">
    select * from teacher where id = #{tid}
</select>
<resultMap id="rTeaAndStu2" type="teacher">
    <collection property="students" javaType="ArrayList" ofType="Student"
                select="queryStudentByTeacherId" column="id"/>
</resultMap>
<select id="queryStudentByTeacherId" resultType="Student">
    select * from student where tid = #{tid}
</select>