if (WebDemoApp.Literal['ziApt_Pmt'] <> '') then
    begin
       sql.Add('AND (prp_MoPriceLR IS NOT Null) AND 
              (prp_MoPriceLR <= ' + WebDemoApp.Literal['ziApt_Pmt'] + ')' );
       sql.Add('AND (prp_MoPriceHR IS NOT Null) AND 
              (prp_MoPriceHR >= ' + WebDemoApp.Literal['ziApt_Pmt'] + ')' );
    end;