Some selections I don't know how to write [closed] - mysql

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I'm new to SQL, so please forgive me if I ask stupid questions.
I have three tables, one with countries, one with cities (connected to countries, with populations...) and one with languages (also connected to countries).
I'd like to ask MySQL about the following informations:
the names of the countries for which all the cities have more than 100000 citizen,
the names of the countries for which at least one city is in the cities table,
the names of the countries where english is spoken, but not spanish,
and so on. I start to understand junctures, a little bit of grouping, but that's about all.

Answer 1

First query
SELECT name FROM country WHERE id IN
(SELECT big_city.country_id FROM
(SELECT country_id, COUNT(*) as n FROM city WHERE population > 100000 GROUP BY country_id) as big_city,
(SELECT country_id, COUNT(*) as n FROM city GROUP BY country_id)
as all_city WHERE big_city.country_id = all_city.country_id AND big_city.n = all_city.n)
What I'm doing here in the subqueries is making a list of countries with all registered towns having a population greater than 100'000 people.
Second query
SELECT country.name FROM country WHERE country.id IN (SELECT DISTINCT country_id FROM city);
Doing so you will get all the country IDs in the city table, so you can use this as a condition
Third query
SELECT country.name FROM country WHERE country.id IN
(SELECT DISTINCT country_id FROM language WHERE language = "en")
AND NOT country.id IN (SELECT DISTINCT country_id FROM language WHERE language = "es")
Same as before, you fetch all the countries in which English or Spanish is spoken and you filter accordingly

Answer 2

Provide more details like tables and database version:
If you consider the following script in SQLServer 2017:
create table countries
(
[id] int not null identity,
[name] varchar(100) not null,
constraint pk_countries primary key ([id])
)
insert into countries ([name]) values ('Country 1'), ('Country 2'), ('Country 3')
create table cities
(
[id] int not null identity,
[idCountry] int not null,
[name] varchar(100) not null,
[population] int not null,
constraint pk_cities primary key ([id]),
constraint fk_cities_countries foreign key ([idCountry]) references countries ([id])
)
insert into cities ([idCountry], [name], [population]) values
(1, 'City 11', 1500000), (1, 'City 22', 2000000),
(2, 'City 21', 2000000), (2, 'City 22', 100)
create table languages
(
[id] int not null identity,
[idCity] int not null,
[name] varchar(100) not null,
constraint pk_languages primary key ([id]),
constraint fk_languages_cities foreign key ([idCity]) references cities ([id])
)
insert into languages ([idCity], [name]) values (1, 'Lang 1'), (1, 'Lang 2'), (1, 'Lang 3')
-- the names of the countries for which all the cities have more than 100000 citizen
select
distinct (a.name)
from
countries a
where
not exists (select * from cities where idCountry = a.id and population < 1000000) and
exists (select * from cities where idCountry = a.id)
go
-- the names of the countries for which at least one city is in the cities table,
select
distinct (a.name)
from
countries a
where
exists (select * from cities where idCountry = a.id)
Results (http://www.sqlfiddle.com/#!18/326e0/1):
Country1
Country 1
Country 2