hibernate 分组查询 count(distinct a, b）

hql语句：

select mag.mag_id,
       count(distinct record.magId, record.articleId, record.screenNum)
from Magazine mag, 
     ArticleTemplateRecord record 
where mag.mag_id=record.magId and 
      mag.brand_id=656 
group by mag.mag_id

报错：
org.hibernate.hql.ast.QuerySyntaxException: expecting CLOSE, found ',' near line 1, column 46

也就是说，distinct record.magId后不希望出现','
请问这用hql该怎么写，别说用sql处理，谢谢！

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from 后面可以同时写两个表么？