sql查找特定流派的電影

Question

select 
    film.title 
from film 
    left outer join filmitem ON film.filmid = filmitem.filmid 
    left outer join filmgenre ON filmitem.filmid = filmgenre.filmid 
where 
    film.title = title and filmgenre.genre NOT IN (
    select genre from genre 
    where genre != 'Comedy' and genre != 'Horror') 
group by title; 

我想找到僅包含流派'喜劇'和'恐怖'的電影。當我運行這個查詢時，我得到了喜劇和其他性別的電影，但我想排除其他性別，只獲得只有喜劇和恐怖的電影。有什麼建議嗎？

Answer 1

select 
    film.title 
from film 
    left outer join filmitem ON film.filmid = filmitem.filmid 
    left outer join filmgenre ON filmitem.filmid = filmgenre.filmid 
where 
    film.title = title and filmgenre.genre IN ('Comedy', 'Horror') 
group by title; 

UPD：啊，對不起，第二次讀你的問題。將更新查詢在一分鐘...

UPD2：如果您需要選擇只有兩個流派「喜劇」和「恐怖」電影，那麼你可以使用

select 
    film.title 
from film 
    left outer join filmitem ON film.filmid = filmitem.filmid 
where 
    film.title = title 
    AND EXISTS (SELECT * FROM filmgenre fg WHERE filmitem.filmid = fg.filmid AND fg.genre='Comedy') 
    AND EXISTS (SELECT * FROM filmgenre fg WHERE filmitem.filmid = fg.filmid AND fg.genre='Horror') 
    AND NOT EXISTS (SELECT * FROM filmgenre fg WHERE filmitem.filmid = fg.filmid AND fg.genre NOT IN ('Comedy','Horror')) 
group by title; 

雖然我很確保有更高效的方法來做到這一點...

Answer 2

如果你只需要電影標題，下面應該提供最佳性能。似乎沒有必要在select語句中加入連接，並且當然不需要將它們留在外連接中。

SELECT Title 
FROM Film 
WHERE FilmID IN (SELECT FilmID FROM FilmGenre WHERE Genre IN ('Comedy', 'Horror')) 

或在某些RDBMS連接是比子查詢更爲有效where子句（Read more...）

SELECT Film.Title 
FROM Film 
     INNER JOIN 
     ( SELECT FilmID 
      FROM FilmGenre 
      WHERE Genre IN ('Comedy', 'Horror') 
      GROUP BY FilmID 
     ) g 
      ON g.FileID = Film.FilmID 

編輯：

如果需要什麼樣的電影是僅喜劇和恐怖然後你需要類似的東西：

SELECT Film.Title 
FROM Film 
     INNER JOIN 
     ( SELECT FilmID 
      FROM FilmGenre 
      GROUP BY FilmID 
      HAVING COUNT(DISTINCT CASE WHEN Genre IN ('Comedy', 'Horror') THEN Genre END) = 2 
      AND COUNT(DISTINCT Genre) = 2 
     ) g 
      ON g.FileID = Film.FilmID 

同樣的邏輯仍然應用根據RDBMS將子查詢移動到IN子句中進行優化。

Answer 3

嘗試：

select title from film f 
where not exists 
(select null 
from filmgenre g 
where f.filmid = g.filmid and 
     g.genre NOT IN ('Comedy', 'Horror') 
) 

（假設總是會有分配給電影的至少一個流派。）

編輯：可替代地，如果有可以是不分配給任何類型的膜，嘗試：

select max(f.title) title 
from film f 
join filmgenre g on f.filmid = g.filmid 
group by f.filmid 
having count(distinct g.genre) = 
     count(distinct case when g.genre in ('Comedy', 'Horror') then g.genre end)