SQL ISNULL(), NVL(), IFNULL() and COALESCE() Functions. Look at the following "Products" table: P_Id ProductName UnitPrice UnitsInStock UnitsOnOrder 1 Jarlsberg 10.45 16 15 2 Mascarpone 32.56 23 3 Gorgonzola 15.67 9 20 Suppose that the "UnitsOnOrder" column is optional, and may contain NULL values. We have the following SELECT statement: SELECT ProductName,UnitPrice*(UnitsInStock+UnitsOnOrder) FROM Products In the example above, if any of the "UnitsOnOrder" values are NULL, the result is NULL. Microsoft's ISNULL() function is used to specify how we want to treat NULL values. The NVL(), IFNULL(), and COALESCE() functions can also be used to achieve the same result. In this case we want NULL values to be zero. Below, if "UnitsOnOrder" is NULL it will not harm the calculation, because ISNULL() returns a zero if the value is NULL: MS Access SELECT ProductName,UnitPrice*(UnitsInStock+IIF(ISNULL(UnitsOnOr