IIf condition in criteria (1 Viewer)

[alktrigger]

I'm trying to create a query that will update as a textbox is filled, but if there is nothing in the textbox I want it to act as if there is no criteria

IIf(len([Forms].[frmMembers].[txtLastName]) > 0 , _
     InStr(1, Left([Forms].[frmMembers].[txtLastName,_
     len([Forms].[frmMembers].[txtLastName])), [COLOR=Red]ShowAll[/COLOR])

What do I replace ShowAll with?

 

[Brianwarnock]

You want the criteria to be based on what is in
[Forms].[frmMembers].[txtLastName]) or if that is null select all of the records?

Where yourfield = [Forms].[frmMembers].[txtLastName] or [Forms].[frmMembers].[txtLastName] is null

Brian