無法讓這個查詢在SQL（Oracle）中工作

Question

我試圖從下面的數據庫（參見下面的關係圖）中返回他們管理的官員姓名，他們管理的酒店以及他們已經參考的匹配數量。

我曾嘗試以下，但它不工作：

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 

我得到一組功能的錯誤選擇，並在年底的case聲明也不起作用。從參考

關係圖：

Answer 1

什麼是你的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, '-')