无法使此查询在SQL（Oracle）中工作

Question

我试图返回官员名称，他们管理的酒店以及他们从以下数据库中查看的匹配数量（请参阅下面的关系图）。

我尝试了以下操作，但它不起作用：

select officials.name as Official,
hotels.name as Hotel, -- hotel the official manages
count (case when officials.name = matches.referee then 1 else null end) as Matchesrefereed
from officials
left join hotels
on  officials.staffid = hotels.manager
left join matches
on officials.staffid = matches.referee
where (case when hotels.name is null then '-' else hotels.name end); -- print '-' if does not manage hotel

我得到select的组函数错误，最后的case语句也不起作用。

参考的关系图：

Answer 1

您的DBMS是什么？

select 
   officials.name as Official,
   nvl(hotels.name, '-') as Hotel, -- hotel the official manages
   count (matches.referee) as Matchesrefereed
  from officials
  left join hotels on  officials.staffid = hotels.manager
  left join matches on officials.staffid = matches.referee
group by officials.name, nvl(hotels.name, '-')