一、动态SQL

1、if

  SELECT * FROM BLOG   WHERE state = ‘ACTIVE’       AND title like #{title}    SELECT * FROM BLOG WHERE state = ‘ACTIVE’       AND title like #{title}        AND author_name like #{author.name}  

2、choose, when, otherwise

相当于switch

  SELECT * FROM BLOG WHERE state = ‘ACTIVE’            AND title like #{title}              AND author_name like #{author.name}              AND featured = 1      

3、trim, where, set

（1）where

  SELECT * FROM BLOG                 state = #{state}                 AND title like #{title}                AND author_name like #{author.name}      

（2）trim

    
       ... 
    

（3）set 元素可以用于动态包含需要更新的列，而舍去其它的

    
       update Author    
           
      
       username=#{username},
            
      
       password=#{password},
            
      
       email=#{email},
            
      
       bio=#{bio}
          
       where id=#{id}
    

4、foreach

动态 SQL 的另外一个常用的操作需求是对一个集合进行遍历，通常是在构建 IN 条件语句的时候

  SELECT *  FROM POST P  WHERE ID in          #{item}  

5、bind

bind 元素可以从 OGNL 表达式中创建一个变量并将其绑定到上下文：

    SELECT * FROM BLOG  WHERE title LIKE #{pattern}