nxql query from studio

Hello, we have to do an nxql query via studio in a content view , but we want to fetch document that starts with the first letter of the currentdocument, so we know that we do as this : where dc:title like 'a%', for example, but the problem is that we want to do a parameter in the Like so it becomes :where dc:title like ? and we have put our parameter as shown in the screenshot.

NOw how to put the % in the parameter so that allow to give the same results as like'a%'?