加入相同的 table 多次，导致双记录

Question

我有主人 table 有 DEPARTURE_CITY,ARRIVAL CITY 等字段。另一个 table secondry_details 包含 city_code 和 city_name。

我想要这样的输出 Departure_city,City_code,Arrival_city,City_code

下面的查询返回恰好两次记录，像交叉连接一样工作

'''select m.Departure_city,s1.City_code as department_city_code,m.Arrival_city,s2.Arrival_city_code 来自大师 table m

左连接secondry_details1 s1 ON m.Departure_city=s1.city_name

左连接 secondry_details1 s2 ON m.Arrival_city=s2.city_name'''

请帮忙。

Answer 1

我检查过这个查询

select 
    m.departure_city, s1.city_code as departure_city_code,
    m.arrival_city,s2.city_code 
from travel_master m
left join secondry_details1 s1 ON m.departure_city = s1.city_name
left join secondry_details1 s2 ON m.arrival_city = s2.city_name;

有：https://www.db-fiddle.com/f/c7uKuWYYTTwZCfqufBC7tv/0 并且按预期工作。