mybatis动态sql:2020-09-17

• 本文只介绍动态mybatis动态sql的使用

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• if元素------------------------------------

        select id,name,age from yang as y
        
            
            
            
                y.name=#{name}
            
            
                and y.id=#{id}
            
        
    

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• where元素(自动拼接关键字)------------------------------------

        select id,name,age from yang as y
        
            
            
            
                y.name=#{name}
            
            
                and y.id=#{id}
            
        
    

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• choose元素------------------------------------

• 注意:when判断不能用中文判断,只能用英文跟数字

        select * from yang as y
        

            

                
                    y.name=#{name}
                
                
                    and y.age=#{age}
                
                
                    y.age=20
                
            
        
    

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• set元素------------------------------------

 
        UPDATE user

        
            
                username = #{username},
            
            
                sex = #{sex},
            
            
                birthday = #{birthday},
            
        
        WHERE id = #{id};
    

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• trim元素------------------------------------

• ​ trim 是更灵活用来去处多余关键字的标签，它可以用来实现 where 和 set 的效果。

• trim代替where

 
    
        SELECT *
        FROM user u
        
        
            
                u.username=#{username}
            
            
                AND u.sex = #{sex}
            
            
                AND u.birthday = #{birthday}
            
        
    

• ​ trim 代替 set

  
  
    UPDATE user  

      
          
            username = #{username},  
          
          
            sex = #{sex},  
          
          
            birthday = #{birthday},  
          
      
    WHERE user_id = #{user_id}  

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• foreach元素------------------------------------

• 单参数List的类型

 
        select * from user where id in

        
            #{item}
        
    

• 单参数array数组的类型

     select * from user where id in

     
          #{item}
     
 

• 自己把参数封装成Map的类型

        select * from user where username like "%"#{username}"%" and id in

        
            #{item}