Queries are an essential part of any database application. Queries are the tools that enable you and your users to extract data from multiple tables, combine it in useful ways, and present it to the user as a datasheet, on a form, or as a printed report.
You may have heard the old cliché, "Queries convert data to information." To a certain extent, this statement is true—that's why it's a cliché. The data contained within tables is not particularly useful because, for the most part, the data in tables appears in no particular order. Also, in a properly normalized database, important information is spread out among several different tables. Queries are what draw these various data sources together and present the combined information in such a way that users can actually work with the data.
In this chapter, you'll learn how to create and enhance queries. Using the Sales (
tblSales), Customers (
tblCustomers), Contacts (
tblContacts), Sales Line Items (
tblSalesLineItems), Categories (
tblCategories), and Products (
tblProducts) example tables, you'll see how to create several types ...