Errors With Wrong Data Type On Search Form

I have a search form that searches through employee records by either employee number or last name. I have 2 radio buttons, one for last name and the other for employee number. The value of those radio buttons tells the query what to search by. My problems is if they forget to select last name and type text into the search field. I get an error of course. How should I handle this? I need some fresh eys on the problem.

If request.QueryString("action") = "search" AND request.form("searchby") = "nam" then
rsTraining.Source = "SELECT * FROM EMPLOYEE WHERE " & searchby & " LIKE '" & criteria & "%' AND STATUS ='Active' ORDER BY NAME_LAST, NAME_FIRST"
End If

If request.QueryString("action") = "search" AND request.form("searchby") = "num" then
rsTraining.Source = "SELECT * FROM EMPLOYEE WHERE " & searchby & " = " & criteria & " AND STATUS ='Active' ORDER BY NAME_LAST, NAME_FIRST"
End If