The concatenation of string values can be a nuisance when referencing fields with Null values, because you want to avoid having extra spaces where the missing string value should have appeared.
A classic example of this is a person's name and their spouse. You want to add the " and Spouse" to the name if the Spouse field is filled.
Here's the data:
|PersonID||First Name||Last Name||Spouse|
And the results we want:
|2||Thomas and Jane Smith|
|3||Jack and Sally Thompson|
If the Spouse field allows zero length string values ("") -- its AllowZeroLength property is True, you need to consider both Nulls and "". You should use the NullToZero function NZ, to handle either case:
SELECT PersonID, FirstName & IIF(Nz(Spouse)<>"", " & " & Spouse) & " " & LastName AS Person
The NZ function evaluates the value it is passed. For text fields, it returns "" if it's null or "". For numeric and dates fields, it returns zero if it's null. This makes it easy to handle nulls in either case.
If the Spouse field does not allow zero length strings, blank values are always null. In this situation, we can avoid using a user-defined/built-in function to test for null. The concatenation of a string value and a null value will return a null value. Thus, you eliminate the extra processing needed:
SELECT PersonID, FirstName & (" and " + Spouse) & " " & LastName AS Person
By using the "+" command to combine the " and " and [Spouse] fields, the result is nothing if the Spouse field is null. This is a difference from using the "&" command which concatenates fields and would leave the " and " if Spouse is null.
Thank you! Thank you! I just finished reading this document, which was part of a link in the recent Buzz newsletter. I have printed it for others to read, especially those skeptical on the powers of Access and its capabilities.