Search By Form: Yes / No / Both

Hello,

Considering the search function will not allow searching for 'yes' 'no' '0' or '-1' because they are too short, I have to ask here:

1st Question:
If providing query criteria by form, how do I set a query to show all records if the search/criteria source is null? This relates directly to the Yes/No problem, if I provide a checkbox to search for items sold, for example, it will only show items sold when clicked, if it is not clicked, it returns zero results.

Is this better handle by an option group on the form? Say Yes (value is -1), No (value is 0), and Both (value Is Null?). If someone could give me direction in both this specific issue, as well as how to best handle Is Null in a search query by form I oul REALLY appreciate it!!!


2nd Question:
How do you set up queries / forms to handle this?

Thank you!!!!