I want that the user can only input unique code-numbers. Now, if he edit a
record, i can't find out, if this number is unique or not (I have textboxes
connected with data-connection).

Pierre

Using the Data Control, you can find out if a number is already used with:

if the data in question is in a variable NewNum

Data1.Recordset.FindFirst "[FieldName] = '" + NewNum + "'"
if Data1.Recordset.NoMatch then
{NewNum was not found in the database}
Else
{Error message}
end if

Alternately, you can add an index to the database table telling the field to
be unique.  Then the program will generate an error if there is a duplicate
value.  You can use error trapping to procede from there