When you need to get data from your database, you naturally start by coding a SELECT statement to return one or more rows—a rowset—containing the answer to your question. Sometimes you want this kind of comprehensive information; other times you simply want a yes or no answer. When you ask, "Are seats available on the next flight to Cleveland?" you're not asking for a list of those seats—only whether seats are obtainable. In some cases, you might want to return a number from a que...