ciao a tutti, vorrei sapere come si fa a fare l'alert quando l'user è già esistente.

codice:
MM_flag="MM_insert"
If (CStr(Request(MM_flag)) <> "") Then
  MM_dupKeyRedirect="insdip.asp"
  MM_rsKeyConnection=MM_autentica_STRING
  MM_dupKeyUsernameValue = CStr(Request.Form("matr"))
  MM_dupKeySQL="SELECT matricola FROM dbo.anagrafica WHERE matricola='" & MM_dupKeyUsernameValue & "'"
  MM_adodbRecordset="ADODB.Recordset"
  set MM_rsKey=Server.CreateObject(MM_adodbRecordset)
  MM_rsKey.ActiveConnection=MM_rsKeyConnection
  MM_rsKey.Source=MM_dupKeySQL
  MM_rsKey.CursorType=0
  MM_rsKey.CursorLocation=2
  MM_rsKey.LockType=3
  MM_rsKey.Open
  If Not MM_rsKey.EOF Or Not MM_rsKey.BOF Then 
     'the username was found - can not add the requested username
        MM_qsChar = "?"
    If (InStr(1,MM_dupKeyRedirect,"?") >= 1) Then MM_qsChar = "&"
    'MM_dupKeyRedirect = MM_dupKeyRedirect & MM_qsChar & "requsername=" & MM_dupKeyUsernameValue
   Response.Write "<script>"
   Response.write "window.alert(' + matr + è già esistente');"
   Response.write "document.form1.matr.value="";"
   Response.Write "</script>"
   ' Response.Redirect(MM_dupKeyRedirect)
  End If
    MM_rsKey.Close
End If
%>
Non ci riesco...........
Grazie
e vorrei che l'alert sia