In a condition with a comparison operator, the expression to the left of the operator is compared to the expression to the right. The outcome is a truth value: True or False.
The != and <> operators are equivalent. They both return True if the expressions evaluate to a different value and False if they evaluate to the same value.
A number value is greater than another number value if it is greater in the mathematical sense. A string value is greater than another string value if it is comes last in alphabetical sort order. A date value is greater than another date/time value if it designates a later date/time.
Comparisons with a NULL value evaluate to False, regardless of the mathematical operator.