I'm sorry for multiple threads. This subject was total misunderstanding by me. The thing that was confusing me was that if I don't enter a search term into the search field then it would not return that record even if some of the fields match. The right way is a dynamic query like this:

(sql (:select '* :from 'kupci :where (:and (:raw (if (parameter "ime") (sql (:like 'ime (concat-string "%" (parameter "ime") "%")))))) (:raw (if (parameter "prezime") (sql (:like 'prezime (concat-string "%" (parameter "prezime") "%"))))))))

I first have to check is the search term even entered into the search field. It finally works.