三、Select语句

Student.java

public class Student {
    private Integer id;
    private String name;
    private String gender;
    private Class clazz;
}

Class.java

public class Class {
    private Integer id;
    private String name;
    private List students;
}

StudentMapper.java

    
    Student selectById(int id);

StudentMapper.xml

    
        
        
        

        
        
    
    
            SELECT
                s.`id` id,
                s.`studentName` NAME,
                s.`gender` gender,
                s.`classId` cid,
                c.`name` cname
            FROM
                tbl_student s
            JOIN
                tbl_class c
            ON
                s.classId = c.id
            WHERe
                s.`id` = #{id}
    
  
3、复杂resultMap映射之association为对象赋值 
 
StudentMapper.java
 
    
    Student queryById(int id);
 
 
StudentMapper.xml
 
    
        
        
        



        
            
            
        
    
    
            SELECT
                s.`id` id,
                s.`studentName` NAME,
                s.`gender` gender,
                s.`classId` cid,
                c.`name` cname
            FROM
                tbl_student s
            JOIN
                tbl_class c
            ON
                s.classId = c.id
            WHERe
                s.`id` = #{id}
    

StudentMapper.java

    
    Student queryByIdStep(Integer id);

ClassMapper.java

    
    Class queryById(Integer id);

ClassMapper.xml

    
        select id,name from tbl_class where id = #{id}
    
 
 
StudentMapper.xml
 
    
        
        
        






        
        
    
    
        select * from tbl_student where id = #{id}
    

ClassMapper.java

    
    Class queryByIdPlus(Integer id);

ClassMapper.xml

    
        
        


        
            
            
            
        
    

    
        SELECT
            c.id cid,c.`name` cname,
            s.`id` sid,s.`studentName` sname,s.`gender` sgender
        FROM
            tbl_class c
        LEFT JOIN
            tbl_student s
        ON
            c.`id` = s.`classId`
        WHERe
            c.id = #{id}
    
  
7、复杂resultMap映射之collection的分步使用 
 
ClassMapper.java
 
    
    Class queryByIdPlusStep(Integer id);
 
 
StudentMapper.java
 
    
    List queryByClassId(Integer cid);
 
 
StudentMapper.xml
 
    
        select * from tbl_student where classId = #{id}
    

ClassMapper.xml

    
        
        

        
    

    
        select * from tbl_class where id = #{id}