sql case when x =？那麼y =？結束

Question

我是一個sql案例的問題，我想檢查一個列值，如果返回true，那麼我想要另一個列值改變，但在'case'中，你只能檢查一列，只改變價值，我如何使它工作？

select f.[film name],f.city,p.[participant name], 
case rt.[type name] 
when 'director' then 'director' else null 
end 'role type' 
from Films f 
join FilmParticipants fp on fp.filmID=f.filmID 
join Participants p on p.participantID=fp.participantID 
join RoleType rt on rt.roleID=fp.roleID 
where f.city in(
select f.city 
from Films f 
group by f.city 
having COUNT(*)>1) 
order by f.city 

它給這個表：

film name | city  | participate name | role type 
Shrek  | London  | John    | null 
Shrek  | London  | John    | null 
Dragon  | London  | Rick    | null 
Drago  | London  | Morty   | Director 

現在我想，只要有在「角色類型列」空的「參與名稱」欄爲空爲好。

Answer 1

你可以使用的情況下當角色類型和顯示partecipant.name

 select f.[film name],f.city, 
     case rt.rt.[type name] 
      when 'director' then p.[participant name] else null end 'partecipant', 
     case rt.[type name] 
      when 'director' then 'director' else null 
     end 'role type' 
     from Films f 
     join FilmParticipants fp on fp.filmID=f.filmID 
     join Participants p on p.participantID=fp.participantID 
     join RoleType rt on rt.roleID=fp.roleID 
     where f.city in(
     select f.city 
     from Films f 
     group by f.city 
     having COUNT(*)>1) 

     order by f.city 

用於去除

 select [film name], city, max(partecipant), max([role type]) 
     from (
     select f.[film name],f.city, 
     case rt.rt.[type name] 
      when 'director' then p.[participant name] else null end 'partecipant', 
     case rt.[type name] 
      when 'director' then 'director' else null 
     end 'role type' 
     from Films f 
     join FilmParticipants fp on fp.filmID=f.filmID 
     join Participants p on p.participantID=fp.participantID 
     join RoleType rt on rt.roleID=fp.roleID 
     where f.city in(
     select f.city 
     from Films f 
     group by f.city 
     having COUNT(*)>1) 
     order by f.city) t 
     group by [film name], city