Question

I have three tables in a Mysql database – countries, cities and hotels. Their relations are: countries hasMany cities and cities hasMany hotels.

I want to be able to select all hotels given a certain countries.id. I am pretty weak in SQL. The join statement i came up with is as follows which always returns 0 rows.

SELECT 
    countries.name as country,
    cities.name as city,
    hotels.name as hotel
FROM 
    countries
    left join cities
        on countries.id = cities.country_id
    left join hotels
        on cities.id = hotels.city_id

WHERE
    countries.id = @id

help?

Answer 1

Try leaving off the where clause and see what records you actually have. Maybe the specific id you’re using is not a known country id.

---

Also, just on a strictly formatting/style issue, IMHO this is better:

SELECT 
    countries.name as country,
    cities.name as city,
    hotels.name as hotel
FROM countries
left join cities on cities.country_id = countries.id
left join hotels on hotels.city_id = cities.id
WHERE countries.id = @id