Introduction
Very simple subqueries
Subqueries with multiple results
Correlated subqueries
Instruction
Wow, cool! Now, remember the operator IN? It allowed us to specify a few values in the WHERE clause, so it worked a bit like the OR operator. Now, take a look:
SELECT * FROM city WHERE country_id IN ( SELECT id FROM country WHERE country.population < 40000 );
Can you predict what the above instruction does? It shows all cities from countries where the total population of the country is less than 40,000.
Exercise
Show all information about all trips to cities which have a rating lower than 4.
Stuck? Here's a hint!
Type:
SELECT * FROM trip WHERE city_id IN ( SELECT id FROM city WHERE rating < 4 );
