在不同的表上加入兩個類似的查詢 - MySQL OR

Question

我在MySQL查詢時遇到了問題（我是一個新手，所以對我來說很簡單！）。我有一個帶有電視節目的網站，並希望根據兩種不同的操作（用於自定義時間表）選擇兩個日期之間播出的節目（沒有問題）。基本上，如果用戶要麼跟隨（uses_follow_shows）或觀看節目（user_watched），我想要顯示該節目，所以我想我會有（query_on_follow或query_on_watch）像下面但不起作用（我得到1200行而不是3，它從user_watched獲取每個現有行）。

我認爲這種說法會做，但它不，我不明白爲什麼

SELECT * FROM show_episode_airdate, show_episode, show_network, network, shows, users_follow_shows, user_watched 
               WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' 
               AND (show_episode.episode_id = show_episode_airdate.episode_id 
               AND shows.id = show_network.show_id 
               AND show_network.network_id = network.network_id 
               AND show_episode.imdb_id_show = shows.imdb_id 
               AND users_follow_shows.user_id = 2 AND shows.id = users_follow_shows.show_id 

               OR user_watched.user_id = 2 
               AND shows.id = user_watched.show_id 
               AND show_episode.episode_id = show_episode_airdate.episode_id 
               AND shows.id = show_network.show_id 
               AND show_network.network_id = network.network_id 
               AND show_episode.imdb_id_show = shows.imdb_id) 
               ORDER by network.network_id ASC 

誰能告訴我有什麼不對？

謝謝！

編輯：

SELECT * 
FROM show_episode_airdate join 
show_episode 
on show_episode.episode_id = show_episode_airdate.episode_id join 
shows 
on shows.imdb_id = show_episode.imdb_id_show join 
show_network 
on show_network.show_id = shows.id join 
network 
on show_network.network_id = network.network_id join 
users_follow_shows 
on shows.id = users_follow_shows.show_id join 
user_watched 
on shows.id = user_watched.show_id 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' and 
    (users_follow_shows.user_id = 2 or 
    user_watched.user_id = 2 
) 
ORDER by network.network_id ASC; 

Answer 1

你需要把()爲OR條件，例如，如果這是你的目標：

SELECT * FROM show_episode_airdate, show_episode, show_network, network, shows, users_follow_shows, user_watched 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' 
AND ((show_episode.episode_id = show_episode_airdate.episode_id 
AND shows.id = show_network.show_id 
AND show_network.network_id = network.network_id 
AND show_episode.imdb_id_show = shows.imdb_id 
AND users_follow_shows.user_id = 2 
AND shows.id = users_follow_shows.show_id) 
OR (user_watched.user_id = 2 
AND shows.id = user_watched.show_id 
AND show_episode.episode_id = show_episode_airdate.episode_id 
AND shows.id = show_network.show_id 
AND show_network.network_id = network.network_id 
AND show_episode.imdb_id_show = shows.imdb_id)) 
ORDER by network.network_id ASC 

所以你會得到：IF BETWEEN日期AND第一（條件）OR秒（條件）

我建議你用JOIN/INNER JOIN，我迷失在所有這些AND中：D

Answer 2

這是由於您在where子句中使用的OR條件。爲合併條件給出適當的假設。

只需嘗試以下查詢。

SELECT * FROM show_episode_airdate, show_episode, show_network, network, shows, users_follow_shows, user_watched 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' 
AND ((show_episode.episode_id = show_episode_airdate.episode_id 
AND shows.id = show_network.show_id 
AND show_network.network_id = network.network_id 
AND show_episode.imdb_id_show = shows.imdb_id 
AND users_follow_shows.user_id = 2 AND shows.id = users_follow_shows.show_id ) 
OR (user_watched.user_id = 2 
AND shows.id = user_watched.show_id 
AND show_episode.episode_id = show_episode_airdate.episode_id 
AND shows.id = show_network.show_id 
AND show_network.network_id = network.network_id 
AND show_episode.imdb_id_show = shows.imdb_id)) 

ORDER by network.network_id ASC 

Answer 3

如果您使用正確的連接語法編寫此代碼，那麼邏輯問題就會消失。結果看起來像這樣：

SELECT * 
FROM show_episode_airdate join 
    show_episode 
    on show_episode.episode_id = show_episode_airdate.episode_id join 
    show_network 
    on show_network.show_id = network.show_id join  <------- THIS IS NOT IN YOUR ORIGINAL LIST 
    network 
    on show_network.network_id = network.network_id join 
    user_follows_shows 
    on shows.id = users_follow_shows.show_id join 
    user_watched 
    on shows.id = user_watched.show_id 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' and 
     (users_follow_shows.user_id = 2 or 
     user_watched.user_id = 2 
    ) 
ORDER by network.network_id ASC; 

有什麼好處？該查詢更容易理解，更容易編寫，更易於理解，並且更不容易犯下可怕的錯誤，如忽略連接條件。 SQL引擎可以更輕鬆地優化它，並且運行速度更快。使用正確的連接語法。

好像要強調我的觀點，原始查詢有7個表格，但只有5個連接條件。這通常意味着你正在做表格之間的笛卡爾積。在這種情況下，我相信它缺少了show_network和shows之間的關係。

編輯：

至少現在，查詢是相當可以理解的。問題是用戶可能會觀看一些節目並可能觀看一些節目。您的查詢是在這兩套產品之間生成笛卡爾產品。更糟糕的是，如果一個節目沒有追隨者或沒有觀察者，那麼它就會退出。

解決此問題的一種方法是將查詢分成兩部分。相反，我會用left outer join S和distinct的select子句中：

SELECT distinct * 
FROM show_episode_airdate join 
show_episode 
on show_episode.episode_id = show_episode_airdate.episode_id join 
shows 
on shows.imdb_id = show_episode.imdb_id_show join 
show_network 
on show_network.show_id = shows.id join 
network 
on show_network.network_id = network.network_id left outer join 
users_follow_shows 
on shows.id = users_follow_shows.show_id left outer join 
user_watched 
on shows.id = user_watched.show_id 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' and 
    (users_follow_shows.user_id = 2 or 
    user_watched.user_id = 2 
) 
ORDER by network.network_id ASC; 

的*應該由你真正想要的列被替換 - 如果你避免users_follow_shows和user_watched列distinct只會工作。 left outer join表示將考慮所有節目。

寫這個的另一種方式 - 擺脫了select子句中distinct的需要 - 就是編寫一個子查詢來組合觀看和隨後的節目。這將刪除重複項，如下所示：

SELECT * 
FROM show_episode_airdate join 
    show_episode 
    on show_episode.episode_id = show_episode_airdate.episode_id join 
    shows 
    on shows.imdb_id = show_episode.imdb_id_show join 
    show_network 
    on show_network.show_id = shows.id join 
    network 
    on show_network.network_id = network.network_id join 
    (select show_id, user_id 
     from users_follow_shows 
     union 
     select show_id, user_id 
     from user_watched 
    ) watch_or_follow 
    on shows.id = watch_or_follow.show_id 
WHERE show_episode_airdate.airdate BETWEEN '2013-07-20' AND '2013-07-27' and 
     watch_or_follow.user_id = 2 
ORDER by network.network_id ASC;