Question

我有两个表，一个是城市（id和城市名称），另一个是城市图片（city_id等）。

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

此外，作为备注，timeline_elements还没有该城市的任何图片。

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表的所有列名称。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, ....

SQL left join只返回一行而不是多行

1 个答案: