|Subqueries, in Oracle, are nothing more than queries within queries and they can be present in the SELECT,
FROM, WHERE, GROUP BY, HAVING, and ORDER BY clauses. Subqueries can not only be used essentially anywhere they come in a wide number of
variations many of which are named such as SIMPLE, CORRELATED, SCALAR, INLINE, and NESTED.
Examples of subqueries can be found throughout the Library but the following links point to places in the Library where you are going
to find specific examples of subquery usage that should acquaint you with most of the constructs.