MySQL：OUTER JOIN和COUNT（）

Question

我有表'海报'，表'评论'和表'拖车'。每个表与一个movieID柱连接，但每个表可以为某些movieIDs是空的：

++ posters_table +++  ++ reviews_table ++  ++ trailers_table ++ 

--itemID--+--filename- --itemID--+--review-- --itemID--+--trailer 
---------------------- --------------------- --------------------- 
----001---+--0-- ----004---+--blalba-- ----002---+--002345-- 
----001---+--0013331-- ----004---+--xlalxa-- ----005---+--005434-- 
----002---+--0020052-- ----005---+--zlalza-- ----001---+--005335-- 

我想COUNT（）为指定movieID海报，评论和拖车数量，如果没有可用的得到0 。

所以，如果我要算movieID = 001，我得到：[ '海报'] = 2/[ '评论'] = 0，[ '拖'] = 1（例如）

有人可以交SQL查询要做到这一点？

Answer 1

select 
    (select count(*) from posters_table where itemId = ?) as posters, 
    (select count(*) from reviews_table where itemId = ?) as reviews, 
    (select count(*) from trailers_table where itemId = ?) as trailers; 

Answer 2

我认为，如果你加入了电影表中的结果集，让计数，然后你可以挑选出次数是否> 0，并给予适当的值：

SELECT movieID, IF(posters.posters_count > 0, posters.posters_count,0) AS posters_total, IF(reviews.reviews_count > 0, reviews.reviews_count,0) AS reviews_total, IF(trailers.trailers_count > 0, trailers.trailers_count,0) AS trailers_total 
FROM movies m 
LEFT JOIN (SELECT itemID,COUNT(*) AS posters_count FROM posters_table WHERE itemID = '001' GROUP BY itemID) posters ON posters.itemID = movies.movieID 
LEFT JOIN (SELECT itemID,COUNT(*) AS reviews_count FROM reviews_table WHERE itemID = '001' GROUP BY itemID) reviews ON reviews.itemID = movies.movieID 
LEFT JOIN (SELECT itemID,COUNT(*) AS trailers_count FROM trailers_table WHERE itemID = '001' GROUP BY itemID) trailers ON trailers.itemID = movies.movieID 
WHERE m.movieID = '001' 

编辑：我更喜欢ar的解决方案。简单得多！

Answer 3

select 
    (select count(P.movieid) from posters P where P.movieid=1), 
    (select count(R.movieid) from reviews R where R.movieid=1), 
    (select count(T.movieid) from trailers T where T.movieid=1) 

这些表格不是“真的”加入，所以你需要三个选择。