6.1: Logical Expressions

Sometimes we need to retrieve data based on multiple criteria which are expressed as logical expressions involving the logical operators and, or, and not. For example, a student using the University database might want to know which courses offered by the Chemistry and Physics departments are not full courses (that is, they are not 6 credit hour courses). The criteria can be restated with emphasis on logical operators:

• • • a course is a Chemistry course or a course is a Physics course,

and

• • • the course has any value for credit hours but not 6.

Such criteria involves and, or, and not. Stating the requirements in natural language may seem easy, but stating these properly in the forms-based Query By Example design window requires specialized knowledge.

MS Access provides a way for us to specify the above using the Criteria and Or lines in the Grid. We will consider each of the operators And, Or, and Not.