How to read all database entries?

This is the code I've got at the moment:

procedure TfrmLogin.performQuery;
begin
 query.SQL.Text := 'SELECT * FROM LoginDatabase';
 query.Open;
end;

procedure TfrmLogin.FormCreate(Sender: TObject);
begin
 con := TFDConnection.Create(nil);
 query := TFDQuery.Create(con);
 con.LoginPrompt := false;
 con.Open('DriverID=SQLite;Database=C:\Users\katiee\Documents\Embarcadero\' +
 'Studio\Projects\ProgramDatabase;');
 query.Connection := con;
 performQuery;

 username := query.FieldByName('Username').AsString;
 passcode := query.FieldByName('Passcode').AsString;
end;

procedure TfrmLogin.btnLoginClick(Sender: TObject);
begin
 if (edtUsername.Text = username) and (edtPasscode.Text = passcode) then
 frmPayInfo.show
 else
 if MessageDlg('The username or password entered is incorrect.', mtWarning,
 [mbOK, mbCancel], 0) = mrCancel then
 frmLogin.Close;
end; 

Right now the code, as it doesn't read all database entries, only allows the first database entry as correct answer.

I need to be able to enter any correct combination of username and pass-code from the database and open the form.