Basic Correlated Subqueries
Correlated subqueries are subqueries that reference one or more columns in the main query. Correlated subqueries depend on information in the main query to run, and thus, cannot be executed on their own.
Correlated subqueries are evaluated in SQL once per row of data retrieved -- a process that takes a lot more computing power and time than a simple subquery.
In this exercise, you will practice using correlated subqueries to examine matches with scores that are extreme outliers for each country -- above 3 times the average score!