五、动态sql

动态SQL

  select * from addresses
  
      
          COUNTRY = #{country}
      
      
          and
          CITY = #{city}
      
  

if 可以加入test=""进行相关判断

where 可以去掉多余的前置and

  update addresses
  
      
        city = #{city},
      

      
         country = #{country},
      

      
          street = #{street},
      

      
          state = #{state},
      

      
          zip = #{zip},
      
  
  
      ADDR_ID = #{addrId}
  

set 除去后面的逗号,

  select * from addresses
  
      
          
              and country = #{country}
          
          
              and state = #{state}
          
          
              and city = #{city}
          
      
  

choose 相当于if.. else if

otherwise 相当于else

  select * from addresses
  
      
          city = #{city} and
      

      
          country = #{country} and
      

      
          street = #{street} and
      

      
          state = #{state} and
      

      
          zip = #{zip} and
      
  

trim 比较全能

可以添加属性，prefix suffix代表前面或后面加额外的sql字段

prefixOverrides suffixOverrides代表前面和后面可能有多余的sql字段

mybatis可以根据属性自己识别

    select *
    from addresses
    
        addr_id in
        
        
          #{item}
        
    

foreach 可以进行遍历

有collection open close item separator index等多种属性

    
    select * from addresses
    
        city like #{_city}
    

bind 可以进行自定义变量

  country,state,city



    select
    
    from addresses

sql 可以取出重复的sql片段进行复用

include 可以导入sql片段

两个标签需要配合使用