mysql - 连接两个表，但如何显示所有结果？

Question

我有两个这样的表结构:

episodes (
episode_id MEDIUMINT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
episode_series_id MEDIUMINT(8) UNSIGNED NOT NULL DEFAULT '0',
episode_series_season TINYINT(2) UNSIGNED NOT NULL DEFAULT '0',
episode_series_episode SMALLINT(5) UNSIGNED NOT NULL DEFAULT '0',
episode_title VARCHAR(200) NOT NULL DEFAULT '',
PRIMARY KEY (episode_id),
KEY series_id (episode_series_id),
KEY episode_series_season (episode_series_season),
KEY episode_series_episode (episode_series_episode)
) ENGINE=MyISAM;

watchlist (
watchlist_id MEDIUMINT(8) UNSIGNED NOT NULL AUTO_INCREMENT,
watchlist_user_id MEDIUMINT(8) UNSIGNED NOT NULL DEFAULT '0',
watchlist_series_id MEDIUMINT(8) UNSIGNED NOT NULL DEFAULT '0',
watchlist_series_episode_id MEDIUMINT(8) UNSIGNED NOT NULL DEFAULT '0',
watchlist_status TINYINT(1) UNSIGNED NOT NULL DEFAULT '0',
PRIMARY KEY (watchlist_id),
KEY watchlist_series_episode_id (watchlist_series_episode_id),
KEY watchlist_series_id (watchlist_series_id)
) ENGINE=MyISAM;"

我想加入这两个，并显示所有结果。

这对我没有帮助:

SELECT e.*, w.* FROM episodes e, watchlist w WHERE e.episode_series_id='1' AND e.episode_series_season='1' AND w.watchlist_user_id='1'

我正在使用这个查询，但像往常一样，它只显示匹配的列(episodes 表中有 30 多行，watchlist 表中有 2 行)

SELECT e.*,w.* FROM episodes e INNER JOIN watchlist w ON e.episode_id=w.watchlist_series_episode_id WHERE e.episode_series_id='1' AND e.episode_series_season='1' AND w.watchlist_user_id='1'

但它只显示 2 行(应该如此)。

episode_id  episode_series_id   episode_series_season   episode_series_episode  episode_title   watchlist_id    watchlist_user_id   watchlist_series_id watchlist_series_episode_id watchlist_status
1                 1                       1                      1                    Pilot            1                 1                    1                    1                        0
2                 1                       1                      2                 Paternity           2                 1                    1                    2                        0 

但我想显示所有匹配结果(我想从这两个表中选择所有列，列出剧集，如果监视列表中有匹配项我想从监视列表列中填充数据，否则它们应该为空)

我想得到这样的结果:

episode_id  episode_series_id   episode_series_season   episode_series_episode  episode_title   watchlist_id    watchlist_user_id   watchlist_series_id watchlist_series_episode_id watchlist_status
1                 1                       1                      1                    Pilot            1                 1                    1                    1                        0
2                 1                       1                      2                 Paternity           2                 1                    1                    2                        0 
3                 1                       1                      3                  whatever1         null             null                 null                 null                      null 
4                 1                       1                      4                  whatever2         null             null                 null                 null                      null 
5                 1                       1                      5                  whatever3         null             null                 null                 null                      null 

我无法将这些放在一起。我该怎么做？

谢谢。

Answer 1

这就是 LEFT JOIN 的用途，而不是 INNER JOIN

SELECT e.*,w.* 
FROM episodes e 
LEFT JOIN watchlist w 
   ON e.episode_id=w.watchlist_series_episode_id AND w.watchlist_user_id='1'
WHERE e.episode_series_id='1' 
AND e.episode_series_season='1' 

• w.watchlist_user_id 的条件也必须出现在 ON 子句中。