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1、一对一

关键字：association 作用：针对pojo对象属性的映射 property：pojo的属性名 javaType：pojo类名 (1) 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集

       
        
        
        
        
            
             
             
             
         
    
       select p.id as personId,p.name,p.sex,p.age,c.*    from tbl_person p,tbl_card c where p.card_id=c.id;

(2) 嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型

column=“引入执行另外定制sql方法的参数值（外键）” select=“执行定制sql方法名” PersonMapper2.xml

          
           
           
           
           
           
       
      select * from tbl_person;   

           
            
        
          select c.id as card_id,c.code from tbl_card c    where c.id=#{
   id};    
           
                
                 
                 
                 
             
        
          SELECT c.id AS card_id, c.code, p.* FROM tbl_card c,tbl_person p WHERE c.id=p.card_id;    

多对一

     select student.id,student.name,teacher.name as tname from student,teacher where student.tid=teacher.id
       
        
        
            
         
    
   
   
     select * from student  select * from teacher where id=#{
   id}
       
        
        
    
   

多对多

商品表、订单表之间就是以多对多关联

商品与订单的关系表 描述多对多的数据表实现 (1)商品pojo:

public class Article implements Serializable {
       private Integer articleId;    private String name;    private Double price;    private String remark;    private List
   
     orders;    省略setter/gettera方法}
   

(2)商品表映射：

ArticleMapper.xml

   
         
                  
                 
                    
                  
             
           
                
                   
           
               
                
              select * from tb_article  where id        in (select article_id from tb_item where order_id=#{
   id})                   
                select * from tb_article  where id=#{
   id}         
   

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