多对一查询：

表结构：

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
)#教师表
CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
)#学生表

实体类：

public class Student {
    private  int id;
    private String name;
    private Teacher teacher;
}

public class Teacher {
    private int id;
    private String name;
}

查询需求：（学生id，学生姓名，教师id，教师姓名）

sql语句：

select *from`student`, `teacher`where`teacher`.`id`=`student`.`tid`;

在mybatis中的接口：

public interface StudentMapper {
    public List getStudent1();
    public List getStudent2();
    public List getStudent3();
}

编写maper文件：

   
        select * from student;
    
    
        
        
        
    
    
        select *from teacher where id=#{id};
    


    
        select s.id sid,s.name sname,t.id tid,t.name tname
        from student s,teacher t
        where s.tid=t.id;
    
    
        
        
        
            
            
        
    

    
        select s.*,t.id tid,t.name tname
        from student s,teacher t
        where s.tid=t.id;
    
    
        
        
    

一对多查询：

实体类：

public class Student {
    private  int id;
    private String name;
    private int tid;
}
public class Teacher {
    private int id;
    private String name;
    private List studentList;
}

接口：

public interface TeacherMapper {
    Teacher getTeacherById1(@Param("tid") int id);
    Teacher getTeacherById2(@Param("tid") int id);
}

xml配置：

    select s.id sid,s.name sname,t.id tid,t.name tname
    from student s,teacher t
    where s.tid=t.id and t.id=#{tid};


    
    
    
        
        
        
    



    select * from teacher where id=#{tid};


    


    select * from student where tid = #{id};