尽管有值，但我不能得到一个用户的值的和时间。

即使用户17有工作时间值，我也会在sumTW列中得到该用户的NULL值。我该怎么解决？

这就是我的查询看起来的样子：

SELECT DISTINCT Hours.*, CASE WHEN SUM(timeWorked) is null then '00:00' ELSE TIME_FORMAT(SUM(timeWorked), '%H:%i') END as sumTW FROM Hours 
WHERE Hours.stampingStatus = 1 GROUP BY Hours.whoWorked

下面是表格代码：

-- phpMyAdmin SQL Dump
-- version 4.9.5
-- https://www.phpmyadmin.net/
--
-- Host: 127.0.0.1:3306
-- Generation Time: Apr 25, 2021 at 01:47 PM
-- Server version: 10.5.9-MariaDB
-- PHP Version: 7.4.16

SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET AUTOCOMMIT = 0;
START TRANSACTION;
SET time_zone = "+00:00";


/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;

--
-- Database: `stud_v20_keser`
--

-- --------------------------------------------------------

--
-- Table structure for table `Hours`
--

CREATE TABLE `Hours` (
  `hourID` int(11) NOT NULL,
  `taskID` int(11) DEFAULT NULL,
  `whoWorked` int(11) NOT NULL,
  `startTime` timestamp NOT NULL DEFAULT current_timestamp(),
  `endTime` timestamp NOT NULL DEFAULT current_timestamp(),
  `timeWorked` time NOT NULL DEFAULT '00:00:00',
  `activated` tinyint(1) NOT NULL DEFAULT 1,
  `location` varchar(30) COLLATE utf8_danish_ci DEFAULT NULL,
  `phaseID` int(11) DEFAULT NULL,
  `absenceType` varchar(30) COLLATE utf8_danish_ci DEFAULT NULL,
  `overtimeType` int(1) DEFAULT NULL,
  `comment` longtext COLLATE utf8_danish_ci DEFAULT NULL,
  `commentBoss` longtext COLLATE utf8_danish_ci DEFAULT NULL,
  `isChanged` tinyint(1) NOT NULL DEFAULT 0,
  `stampingStatus` tinyint(1) NOT NULL DEFAULT 0,
  `taskType` varchar(30) COLLATE utf8_danish_ci NOT NULL DEFAULT 'Definert oppgave'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_danish_ci;

--
-- Dumping data for table `Hours`
--

INSERT INTO `Hours` (`hourID`, `taskID`, `whoWorked`, `startTime`, `endTime`, `timeWorked`, `activated`, `location`, `phaseID`, `absenceType`, `overtimeType`, `comment`, `commentBoss`, `isChanged`, `stampingStatus`, `taskType`) VALUES
(295, 24, 1, '2021-04-22 12:02:46', '2021-04-22 16:02:50', '04:00:04', 1, 'sdf', NULL, NULL, NULL, 'Veldig bra\r\n', 'Flott', 1, 1, 'Prosjekt'),
(299, 33, 3, '2021-04-24 14:43:01', '2021-04-24 14:43:10', '00:00:09', 1, 'Andre Verdenskrig', NULL, NULL, NULL, NULL, NULL, 0, 1, 'Prosjekt'),
(298, 24, 4, '2021-04-22 11:00:00', '2021-04-23 16:00:00', '29:00:00', 1, 'kj', NULL, NULL, NULL, NULL, NULL, 1, 1, 'Prosjekt'),
(300, NULL, 16, '2021-04-24 18:08:58', '2021-04-24 20:09:03', '02:00:05', 1, 'Hjemme', NULL, NULL, NULL, 'asdadsasdasda', NULL, 0, 1, 'Administrativt'),
(301, 35, 16, '2021-04-24 18:09:27', '2021-04-24 21:09:36', '03:00:09', 1, 'Mac', NULL, NULL, NULL, NULL, NULL, 0, 1, 'Prosjekt'),
(302, NULL, 17, '2021-04-24 18:16:31', '2021-04-24 20:18:03', '02:01:32', 1, 'New New York', NULL, NULL, NULL, NULL, NULL, 0, 1, 'Prosjekt'),
(303, NULL, 17, '2021-04-24 18:18:18', '2021-04-24 20:21:59', '02:03:41', 1, 'New New York', NULL, NULL, NULL, NULL, NULL, 0, 1, 'Prosjekt');

--
-- Triggers `Hours`
--
DELIMITER $$
CREATE TRIGGER `calculateTimeWorked` BEFORE UPDATE ON `Hours` FOR EACH ROW SET NEW.timeWorked = TIMEDIFF(new.endTime, new.startTime)
$$
DELIMITER ;

--
-- Indexes for dumped tables
--

--
-- Indexes for table `Hours`
--
ALTER TABLE `Hours`
  ADD PRIMARY KEY (`hourID`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `Hours`
--
ALTER TABLE `Hours`
  MODIFY `hourID` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=304;

--
-- Constraints for dumped tables
--


/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;

（这个表和原来的不一样，原来的有外键。我去掉它们只是为了能够再现同样的问题，同样的问题被报告了）。