無法使該查詢在SQL（Oracle）中工作

Question

我試圖返回官員姓名，他們管理的酒店以及他們從以下數據庫中引用的匹配數（請參見下面的關系圖）。

我已經嘗試了以下方法，但是不起作用：

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

我在選擇時遇到了一個組函數錯誤，並且最后的case語句也不起作用。

參考關系圖：

Answer 1

什么是您的DBMS？

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, '-')