The arithmetic calculation in the query design grid returns a Null (blank) value.

If you use an arithmetic operator (such as +, -, *, /) in an expression, such as [UnitsInStock]+[UnitsOnOrder], and one of the fields in the expression contains a Null value, then the result of the entire expression will be a Null value. To avoid this, you can convert Null values to zeros or other numbers. For more information, click .