Excerpted from Chapter 3: Working with Data in MySQL from the MySQL, 3rd Edition by Paul Dubois. ISBN 0672326736, Copyright © 2005. Used with the permission of Sams Publishing.
VIRTUALLY EVERYTHING YOU DO in MySQL involves data in some way or another because the purpose of a database management system is, by definition, to manage data. Even a simple SELECT 1 statement involves expression evaluation to produce an integer data value.
The article continues at