If .. Else on Button Click !!

Question

Hi There,

 

I have attached code for button click and now need to put the conditon where on if user does not select any filter then should give entire record what i have for select statement.

 

i.e. i am not selecting the listbox values and directly clicking on button then must to give all records of query vise versa works for listbox filter even.

 

Pls help here !!