What are Boolean operators?

Boolean operators are expressions such as AND, OR, NEITHER, and NOR that allow you to add multiple criteria to a query. They take their name from George Boole, the mathematician who first used them.

If you had a T-shirt store with an Base database, for instance, and you wanted to find out how many of your California customers had ordered blue T-shirts, you'd employ the AND operator in your query:

customers from California
AND
who also bought blue T-shirts

If you wanted to see how many customers were from California (these California customers could have bought T-shirts of any color),

and how many customers bought blue T-shirts (these blue T-shirt customers could be from anywhere),

you'd employ the OR operator:

customers from California
OR
customers who bought blue T-shirts