SQL 左連接只返回一行而不是多行

Question

我有兩張表，一張是城市（id 和城市名稱），一張是城市圖片（city_id 等）。

假設我正在尋找名為錫比烏的城市。 那應該返回 3 個結果，因為表中有更多類似的城市（Miercurea Sibiului、Sibiu、Poiana Sibiului），但它只返回一個。

另外，請注意，timeline_elements 還沒有城市的任何圖片。

SELECT cities_countries.*, COUNT(timeline_elements.city_id) as number_of_photos 
FROM cities_countries   
LEFT JOIN timeline_elements on (cities_countries.id = timeline_elements.city_id)
WHERE cities_countries.name LIKE '%Sibiu%'

Answer 1

添加GROUP BY並明確提及cities_countries表的所​​有列名。 我認為這些是cities_countries表中的列。 id, city_id, city_name 。

還為每個表設置別名以提高可讀性。

SELECT C.id, C.city_id, C.city_name, ....
       , COUNT(T.city_id) as number_of_photos 
FROM cities_countries C  
LEFT JOIN timeline_elements T ON C.id = T.city_id
WHERE C.name LIKE '%Sibiu%'
GROUP BY C.id, C.city_id, C.city_name, ....