The outer PROC SQL query retrieves data from the view descriptor; the subquery uses a Pass-Through query to retrieve data. This query returns the names of employees who earn less than the average ...

Read this SQL tutorial to learn when to use SELECT, JOIN, subselects and UNION to access multiple tables with a single statement.

The basic concept of recursion is straightforward: a given chunk of code calls itself until some boundary condition is reached. Arthur Fuller demonstrates how to use recursion in T-SQL.