mysql連接空行？

Question

我有這個疑問

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

，但我想查詢返回從城市所有的城市，即使他們沒有與之相關的city_date？

Answer 1

看到外連接;）（右/左/ FULL）

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