3. Get to know the data - tables city and mountain
Very simple subqueries
Subqueries with multiple results
Correlated subqueries
Other subqueries


Alright, let's move on and check out the table city. There are different cities in each country, so the table gathers information about them. It gives you the id of the city and its name, the id of the country where it can be found, the city population, the area in square kilometers and the rating, where 5 means 'no better place to visit on Earth' and 1 means 'boring as hell'.

How about the table mountain? In each country there are some mountains, so the travel agency gathers information on them too. The table stores columns with the id, the name of the mountain, its height in meters and the id of the country where it is located.

Not much happening here. Why don't we move on?


  1. Open the Database tab on the right.
  2. Take a look at table city.
  3. The take a look at table mountain.
  4. When you're done, click Next exercise to proceed.