Count使用时提示异常

Count使用时提示错误
表score (ID,UserID,PaperID,PaperName,Score)

 SELECT  
  PaperName ,
  UserID ,
  Score ,
  RANK() OVER ( PARTITION BY PaperName ORDER BY Score DESC ) AS 名次
   
FROM Score where PaperName='测试1' 

可以查询出测试1的考生名次，但是我希望加一列参加考试1的总人数：
 SELECT  
  count(PaperName),
  PaperName ,
  UserID ,
  Score ,
  RANK() OVER ( PARTITION BY PaperName ORDER BY Score DESC ) AS 名次
   
FROM Score where PaperName='测试1' 

加了count(PaperName) 出现提示消息 8120，级别 16，状态 1，第 1 行
选择列表中的列 'Score.PaperName' 无效，因为该列没有包含在聚合函数或 GROUP BY 子句中。
请大虾帮我找找原因

[解决办法]

SQL code

SELECT  b.CNT ,  Score.PaperName ,  UserID ,  Score ,  RANK() OVER ( PARTITION BY Score.PaperName ORDER BY Score DESC ) AS 名次FROM Score inner join (select PaperName,CNT=count(1) from score(nolock) group by PaperName) b on score.PaperName=b.PaperNamewhere Score.PaperName='测试1'