Evaluation Precedence

When a WHERE clause is processed, the operators are evaluated in the following order of precedence:

  • Parentheses have the highest precedence.

  • The AND operator has the next level of precedence.

  • The OR operator has the lowest level of precedence.

What does this mean? Well, look at the WHERE clause in Listing 6.9. The clause reads WHERE FirstName='Ben' AND LastName='Forta' OR FirstName='Rick' AND LastName='Richards'. AND is evaluated before OR so this statement looks for Ben Forta and Rick Richards, which is what we wanted.

But what would be returned by a WHERE clause of WHERE FirstName='Rick' OR FirstName='Ben' AND LastName= 'Forta'? Does that statement mean anyone whose first name is either Rick or Ben, and whose last name ...

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