Question

I have five tables:

models:             id, name, specification
models_networks:    id, model_id, network_id
networks:           id, name, description
countries_networks: id, country_id, network_id
countries:          id, countryName, etc, etc

• the models table is connected to the networks table via models_networks with a many to many relation.
• the networks table is connected to the countries table via countries_networks with a many to many relation

I need to do the following query, but I’m stuck:

Select all the models that will work in a specific country.

e.g.: say France has two networks. PigNetwork and CowNetwork. I want to get all the models that work on PigNetwork or CowNetwork, basically any that work in that country one way or the other.

If I’ve made myself clear, can someone help with the JOIN query please? I’ve only ever gone as far as joining two tables before. Thanks.

Answer 1

SELECT
  m.name AS model_name,
  c.countryName,
  COUNT(*) AS network_count
FROM
  models                        AS  m
  INNER JOIN models_networks    AS mn ON mn.model_id = m.id
  INNER JOIN networks           AS  n ON n.id = mn.network_id
  INNER JOIN countries_networks AS cn ON cn.network_id = n.id
  INNER JOIN countries          AS  c ON c.id = cn.country_id
WHERE
  c.countryName = 'France'
GROUP BY
  m.name,
  c.countryName