DreamWeaver parameters HELP

Hello to all, I hope you can help me...

I am using Dreamweaver CS6 and constructing a web site with a multi search form. I have a select box that has VALUE (integer) and Labels. When I choose one field of the select box, and pressing SUBMIT, goes to a result page, showing all records relative with the VALUE I chose. I have used these settings in the recordset:

Edit Variable:

name: modelsearch

Type: Integer (integer is in database too)

Default value: -1

Runtime Value: $_GET['Makes'] (the name of the select box)

and above

... WHERE allcars.all_make=modelsearch

When I choose sth all is ok, but I want when I choose NOTHING on the select box, by pressing the SUBMIT to show me all records..

Please heeeeeeelp

Thank you