query :=TSQLQuery.Create(Self);

query :=TSQLQuery.Create(Self);
   try
      query.SQLConnection := MSSQL_sys;
      query.SQL.Add('SELECT UserName,Pass FROM Register  ') ;
      query.SQL.Add('WHERE Register.UserName=:f1 ') ;
      query.Params[0].AsString := _UserName ;
      query.Open;

      FormMain.Debug(['query.RowsAffected : ',query.RowsAffected],'?');

      getUserName :=query.FieldByName('UserName').AsString;
      getPass :=query.FieldByName('Pass').AsString;

      FormMain.Debug(['getUserName: ',getUserName],'?');
      FormMain.Debug(['getPass: ',getPass],'?');
   finally
      query.Free;
   end;


Why query.RowsAffected always return 0;  And  "recordcount" property not support in this,
How can I get rowAffected in this?