Question

I have a VBA function IsValidEmail() that returns a boolean. I have a query that calls this function: Expr1: IsValidEmail([E-Mail]). When I run the query, it shows -1 for True and 0 for False. So far so good.

Now I want to filter the query to only show invalid emails. I’m using the Query Designer, so I just add a value of 0 to the Criteria field. This gives me a “Data Type Mismatch” error. So does "0" (with quotes) and False. How am I supposed to specify criteria for a boolean function?

Answer 1

The error was caused by the fact that some of the records in my table have a null E-Mail. My query has a where condition to exclude null E-Mail records, so when I ran it with no condition on the IsValidEmail column my function was only called for records with a non-null E-Mail. However, when I added the condition on IsValidEmail it called the function for every record, and the error came from trying to pass null to a function expecting a string.

Another way to say all that:

SELECT [E-Mail],
       IsValidEmail([E-Mail]) <--Executed only for rows matching where clause
FROM   Contacts
WHERE  IsValidEmail([E-Mail]) = False; <-- Gets executed for all rows

Changing my query expression from IsValidEmail([E-Mail]) to IsValidEmail(nz([E-Mail],"X")) resolved the issue.