Harry, you are correct. I'm used to working with NZ in VBA code, not queries. In VBA code, the DEFAULT value of that second parameter is ZERO if you're working with a number type (such as an ID) otherwise it's a zero-length string. MOST of the time I'm working with NZ it's for looking up IDs to see if records exist, so you don't need to specify it.

From Microsoft's Help: If the value of the variant argument is Null, the Nz function returns the number zero or a zero-length string (always returns a zero-length string when used in a query expression), depending on whether the context indicates the value should be a number or a string. If the optional valueifnull argument is included, then the Nz function will return the value specified by that argument if the variant argument is Null. When used in a query expression, the Nz function should always include the valueifnull argument.

So, ideally, when working with queries, always make sure to specify the zero. Thank you, Harry.