数据库中存储单个字符串，前端传多个字符串组成一个字符串，怎么处理查询语句

<if test='a.stageCode != null and a.stageCode != ""'>
  t.stage_code in
  <foreach collection="a.stageCode.split(',')" open="(" close=")" separator="," item="item">
  #{item}
  </foreach>
</if>