title: Mybatis dynamic column in select statement
body: <p>I'm trying to select dynamic column. Below are my codes:</p>
  
  <pre><code>//call the dao method
  String columns = "first_name";
  userDao.sample(1, columns);
  
  //call mapper
  List&lt;User&gt; sample(@Param("userId") int userId, @Param("columns") String columns);
  
  //mapper
  &lt;select id="sample" resultMap="user" parameterType="map"&gt;
      SELECT
          #{columns}
      FROM
          user
      WHERE
          userId = #{userId}
  &lt;/select&gt;
  </code></pre>
  
  <p>This is the result I'm getting:</p>
  
  <p>[null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null]</p>
  
  <p>What am I doing wrong?</p>