In this exercise, you'll see how some queries can be written using either a join or a subquery.
You have seen previously how to use GROUP BY
with aggregate functions and an inner join to get summarized information from multiple tables.
The code given in query.sql selects the top nine countries in terms of number of cities appearing in the cities
table. Recall that this corresponds to the most populous cities in the world. Your task will be to convert the commented out code to get the same result as the code shown.