How to let a query omit the search key sometimes

[Guest]

I have built a search function with a query. I have a form with a ComboBox to let me select the key I want to search. After I press a CmdButton, a result form is open through a query.
My first problem is if I want to omit the key sometimes, that is to retrieve all data, How can do it
My second problem is how to let a message show up if no data is found?
Thank you.

 

[John Vinson]

I have built a search function with a query. I have a form with a ComboBox to let me select the key I want to search. After I press a CmdButton, a result form is open through a query.
My first problem is if I want to omit the key sometimes, that is to retrieve all data, How can do it?

Use a criterion of

=Forms!formname!comboname OR Forms!formname!comboname IS NULL

 

[Guest]

Thank you, John. I've got it.