The SQL NOT operator returns the opposite of the Boolean value it precedes. The following truth table shows all combinations of values for the condition (NOT A)
Notice that for the whenever A is TRUE the result is FALSE, and vice versa.
We can use this to our favor when writing queries. Consider the situation where you may need to match the opposite of a condition…
This query returns People not having a FirstName or Gail or John:
SELECT BusinessEntityId, PersonType, FirstName, LastName FROM Person.Person WHERE NOT (FirstName = 'Gail' or FirstName = 'John')
SQL NOT Operator Resources
To learn more about the SQL NOT Operator, check out these useful resources: