Summary
Today, you performed dozens of exercises involving subqueries. By doing this, you have learned how to use one of the most important parts of SQL. The subquery is a method for placing additional conditions on the data returned by your query. A subquery provides great flexibility in defining conditions, especially conditions for which you do not know the exact value. For example, I might want to get a list of all the products priced above average, but I might not know what the overall average price is offhand. I can include a subquery that calculates the average price.
Today, you also tackled one of the most difficult parts of SQL: a correlated subquery. The correlated subquery creates a relationship between the query and the subquery, ...
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