SQL 左连接只返回一行而不是多行

Question

我有两张表，一张是城市（id 和城市名称），一张是城市图片（city_id 等）。

假设我正在寻找名为锡比乌的城市。 那应该返回 3 个结果，因为表中有更多类似的城市（Miercurea Sibiului、Sibiu、Poiana Sibiului），但它只返回一个。

另外，请注意，timeline_elements 还没有城市的任何图片。

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并明确提及cities_countries表的所​​有列名。 我认为这些是cities_countries表中的列。 id, city_id, city_name 。

还为每个表设置别名以提高可读性。

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, ....