Expression

Expression functions evaluate one or more expressions and return a value — conditional logic and null handling such as CASE-style choices, COALESCE and NULLIF.

Function	Description
COALESCE	Evaluates the arguments in order and returns the current value of the first expression that initially does not evaluate to NULL.
IIF	Returns one of two values, depending on whether the Boolean expression evaluates to true or false.
ISNULL	Replaces NULL with the specified replacement value.
NULLIF	Returns a null value if the two specified expressions are equal.