Introduction
Very simple subqueries
Subqueries with multiple results
Correlated subqueries
Instruction
Good! Remember the NOT operator? We can use it together with EXISTS. Take a look:
SELECT *
FROM city
WHERE NOT EXISTS (
SELECT
*
FROM trip
WHERE city_id = city.id
);
As you probably expect, this query will find all cities that don't have a trip organized to them.
Exercise
Select all mountains with no hiking trips to them.
Stuck? Here's a hint!
Type:
SELECT * FROM mountain WHERE NOT EXISTS ( SELECT * FROM hiking_trip WHERE mountain_id = mountain.id );
