mybatis 动态 sql

  
<update id="updateAuthorIfNecessary">
  
update Author
  
<set>
  
<if test="username != null">username=#{username},</if>
  
<if test="password != null">password=#{password},</if>
  
<if test="email != null">email=#{email},</if>
  
<if test="bio != null">bio=#{bio}</if>
  
</set>
  
where id=#{id}
  
</update>