MYSQL LEFT JOIN不顯示空行

Question

我有2張桌子。 comforts_posts包含所有可用的comfortities和property_amenities，僅包含property設施。 我想運行一個聯接查詢，如果在properties_amenities中未找到行，則將返回帶有NULL的comforts_posts中的所有行。

當前查詢：

SELECT properties_amenities.*, amenities_posts.type, amenities_posts.grouped, amenities_posts.title, properties_amenities.property_id 
FROM properties_amenities 
LEFT JOIN amenities_posts ON properties_amenities.amenity_id = amenities_posts.id
WHERE properties_amenities.property_id=318 OR properties_amenities.property_id IS NULL 
ORDER BY amenities_posts.grouped DESC, amenities_posts.sortby ASC;

此查詢僅返回來自properties_amenities行，而不是所有帶有null的便利設施行。

Answer 1

如果要顯示commendations_posts中的所有行，則需要在LEFT JOIN的左側 。

...
FROM amenities_posts
LEFT JOIN properties_amenities ...

左聯接從左側選擇所有行，而僅從右側選擇匹配的行。