MyBatis的foreach标签与SUM函数同时使用

最近在项目中遇到一个，需要根据传入的存有id的list，计算值，再起别名

<if test="channelList != null and channelList.size()>0">
        <foreach collection="channelList" index="index" item="item" open="" separator="," close="">
        SUM(CASE WHEN ccs.sub_type =#{item} AND ccs.type = 1 THEN ccs.num ELSE 0 END) AS 'dispatchNum${item}'
         </foreach>
</if>