Q:在多人使用的環境下如何確保主鍵值為唯一? 亦即如何產生唯一的鍵值?
A:參考以下程式碼, 由 Bill Todd (TeamB) 提供

function dgGetUniqueNumber(LastNumberTbl: TTable): LongInt;
{Gets the next value from a one field one record
 table which stores the last used value in its first
 field.  The parameter LastNumberTbl is the table
 that contains the last used number.}
const
  ntMaxTries = 100;
var
  I,
  WaitCount,
  Tries:         Integer;
  RecordLocked:  Boolean;
  ErrorMsg:      String;
begin
  Result := 0;
  Tries := 0;
  with LastNumberTbl do
  begin
    {Make sure the table contains a record.  If not, add
     one and set the first field to zero.}
    if RecordCount = 0 then
    begin
      Insert;
      Fields[0].AsInteger := 0;
      Post;
    end; file://if
    {Try to put the table that holds the last used
     number into edit mode. If calling Edit raises
     an exception wait a random period and try again.}
    Randomize;
    while Tries < ntMaxTries do
      try
        Inc(Tries);
        Edit;
        Break;
      except
        on E: EDBEngineError do
          {The call to Edit failed because the record
           could not be locked.}
          begin
            {See if the lock failed because the record is locked by
             another user.}
            RecordLocked := False;
            for I := 0 to Pred(E.ErrorCount) do
              if E.Errors[I].ErrorCode = 10241 then RecordLocked := True;
            if RecordLocked then
            begin
              {Wait for a random period and try again.}
              WaitCount := Random(20);
              for I := 1 to WaitCount do
                Application.ProcessMessages;
              Continue;
            end else
            begin
              {The record lock failed for some reason other than another
               user has the record locked. Display the BDE error stack
               and exit.}
              ErrorMsg := '';
              for I := 0 to Pred(E.ErrorCount) do
                ErrorMsg := ErrorMsg + E.Errors[I].Message +
                  ' (' + IntToStr(E.Errors[I].ErrorCode) + '). ';
              MessageDlg(ErrorMsg, mtError, [mbOK], 0);
              Exit;
            end; file://if
          end;
      end; {try}
    if State = dsEdit then
    begin
      Result := Fields[0].AsInteger + 1;
      Fields[0].AsInteger := Result;
      Post;
    end
    else
      {If the record could not be locked after the
       specified number of tries raise an exception.}
      raise Exception.Create('Cannot get next unique number.
(dgGetUniqueNumber)');
  end;
end;