MyBatis的动态sql_set与if结合的动态更新源码

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cn.mybatis.dao.EmployeeMapperDynamicSQL">
  
	<!-- public void updateEmp(Employee employee); -->
	<update id="updateEmp">
	
	<!-- set方法的使用
	   
	  update tbl_employee 
	  <set>
	<if test="lastName!=null">
		last_name=#{lastName},
     </if>
	<if test="email!=null">
		email=#{email},
     </if>
	<if test="gender!=null">
		gender=#{gender} 
     </if>
     </set>
		where id=#{id}
	</update>
	-->
	
	<!-- 更新拼串 -->
	  update tbl_employee 
	  <trim prefix="set" suffixOverrides=",">
	<if test="lastName!=null">
		last_name=#{lastName},
     </if>
	<if test="email!=null">
		email=#{email},
     </if>
	<if test="gender!=null">
		gender=#{gender} 
     </if>
	</trim>
	where id=#{id}	
	</update>
	
</mapper>