＃1111在SQL中使用组函数无效：Concept？

Question

我正在尝试运行下面的sql代码，它会生成最近3天的平均问题。但是，我越来越#1111 invalid use of group function error。不知道我错在哪里。即使我将该群组删除，此操作仍会保留。请帮忙。

select BookId, ChapterName, AuthorCountry, 
     avg(sum(No_of_issues)) as last3dayavgissues 
from library_data 
where Date between (select max(Date) from library_data) and 
        (select (max(Date)-3) from library_data) 
group by BookId, ChapterName 
having (AuthorCountry='US' OR AuthorCountry='DE')) 
group by BookId, ChapterName 
order by AuthorName 
into outfile 'C:/output files/abc.csv' 
     fields terminated by '\t' 
     lines terminated by '\n'; 

感谢 阿维

Answer 1

使用AVG函数内部和函数的导致无效使用组功能error.sum函数返回只有一个值和单值平均是没有意义的。