mysql加入空行？

Question

我有这个查询

SELECT cities.city, city_date.date_avail 
FROM cities, city_date 
WHERE city_date.city_id = cities.id;

但我想查询从城市返回所有城市，即使他们没有与之关联的city_date？

Answer 1

参见OUTER JOINS;）（RIGHT / LEFT / FULL）

SELECT cities.city, city_date.date_avail
FROM cities
LEFT OUTER JOIN city_date ON city_date.city_id = cities.id;