In order to really understand how to create complex queries, we need a basic knowledge of Boolean Algebra. But a word of advice to those of you who are not that mathematically oriented and who shudder at the thought of anything related to Algebra – don’t panic. Boolean Algebra is not that difficult to grasp and makes perfect sense once you’ve got the basics.

Boolean Algebra is simply a way of rephrasing a complicated logical statement into a series of simpler AND, OR and NOT conditions without changing its meaning. The rules of Boolean Algebra are straight-forward, and can be applied to any logical expression. The notational system was developed by the English mathematician George Boole to permit an algebraic manipulation of logical statements. Today, all computers employ Boole's logic system - using microchips that contain thousands of tiny electronic switches arranged into logical ‘gates’ that produce predictable and reliable conclusions.

For the purposes of trying to understand the 3 Boolean operators, namely AND, OR and NOT, let’s look at 2 simple sets of data, namely

Blue Set (Dark Shading): Contacts whose Job Title = (is exactly) Marketing Manager

Yellow Set (Light Shading): Contacts whose Country = (is exactly) United States of America

Boolean AND

When the AND operator is used to join the 2 sets, the results retrieved will contain both Blue and Yellow information. So in this case you would only get contacts that are Marketing Managers AND have United States of America as their country. This would be the Green set shown above.

Boolean OR

When the OR operator is used to join the 2 sets, the results retrieved will contain either Blue, or Yellow, or Blue and Yellow information together. So in this case you would get contacts that are Marketing Managers or have United States of America as their country, or both. This would be the entire set of Blue, Green and Yellow shown above.

Boolean NOT

When 2 conditions are combined with a NOT operator, the results retrieved will contain only Blue exclusively. So in this case you would get contacts that are Marketing Managers but do not have United States of America as their country. This would be the Blue set above.