Final answer:
A common table expression (CTE) creates a temporary result set that can be referenced within the scope of a single SQL statement to simplify complex queries.
Step-by-step explanation:
A common table expression (CTE) creates a temporary result set that can be used by a query that follows the CTE. This temporary result set is typically used to simplify complex queries by breaking down the query into simpler blocks, which can make the SQL statement more readable and potentially improve performance. Think of a CTE as a temporary view that exists only during the execution of the query.
For example, if you're working with a database and you want to organize a list of sales by region before you aggregate the totals, you could use a CTE to create a list of all sales per region and then use another query to aggregate this data. The CTE acts as an intermediary, non-persistent table that can be referenced within the scope of a single SQL statement.