获取所有用户的下载详细信息

【问题标题】：Fetch all users' download details获取所有用户的下载详细信息
【发布时间】：2020-06-19 09:16:13
【问题描述】：

我的表结构---

--
-- Database: `sample`
--
CREATE DATABASE IF NOT EXISTS `sample` DEFAULT CHARACTER SET latin1 COLLATE latin1_swedish_ci;
USE `sample`;

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

--
-- Table structure for table `downloads`
--

DROP TABLE IF EXISTS `downloads`;
CREATE TABLE IF NOT EXISTS `downloads` (
  `dload_id` int(11) NOT NULL AUTO_INCREMENT,
  `wall_id` int(11) NOT NULL,
  `dload_date` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`dload_id`)
) ENGINE=MyISAM AUTO_INCREMENT=88 DEFAULT CHARSET=latin1;


--
-- Table structure for table `users`
--

DROP TABLE IF EXISTS `users`;
CREATE TABLE IF NOT EXISTS `users` (
  `user_id` int(11) NOT NULL AUTO_INCREMENT,
  `login` varchar(45) DEFAULT NULL,
  `password` varchar(45) DEFAULT NULL,
  `folder_id` varchar(45) DEFAULT NULL,
  `last_login` varchar(45) DEFAULT NULL,
  `status` set('0','1') NOT NULL DEFAULT '1',
  PRIMARY KEY (`user_id`),
  UNIQUE KEY `folder_id_UNIQUE` (`folder_id`),
  UNIQUE KEY `login_UNIQUE` (`login`)
) ENGINE=MyISAM AUTO_INCREMENT=11 DEFAULT CHARSET=latin1;

--
-- Table structure for table `wallpapers`
--

DROP TABLE IF EXISTS `wallpapers`;
CREATE TABLE IF NOT EXISTS `wallpapers` (
  `wall_id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `filename` varchar(100) DEFAULT NULL,
  `upload_date` datetime DEFAULT CURRENT_TIMESTAMP,
  `status` set('0','1') DEFAULT '',
  PRIMARY KEY (`wall_id`)
) ENGINE=MyISAM AUTO_INCREMENT=21 DEFAULT CHARSET=latin1;
  • “用户”包含用户的登录详细信息等。
  • “壁纸”包含用户上传的壁纸和
  • “下载”包含在线用户下载的壁纸。

SELECT U.user_id, U.login, D.dload_id, W.filename, IFNULL(COUNT(D.dload_id), 0) AS total_downloads

FROM 下载 AS D

左加入壁纸 W.wall_id = D.wall_id

LEFT JOIN users AS U on W.user_id = U.user_id

“2020-01-01 00:00:00”和“2020-01-31 00:00:00”之间的 D.dload_date 位置

按 U.user_id、文件名分组

按用户 ID ASC 排序 限制 500

上述查询仅返回已下载壁纸的用户的数据，但我需要列出我的用户表中的所有用户，无论他们的壁纸是否已下载。

查询结果上方

-

预期结果

谢谢

样本数据

INSERT INTO `downloads` (`dload_id`, `wall_id`, `dload_date`) VALUES
(1, 1, '2020-01-01 00:00:00'),
(2, 7, '2020-01-01 00:00:00'),
(3, 7, '2020-01-01 00:00:00'),
(4, 7, '2020-01-01 00:00:00'),
(5, 6, '2020-01-02 00:00:00'),
(6, 7, '2020-01-02 00:00:00'),
(7, 6, '2020-01-02 00:00:00'),
(8, 6, '2020-01-02 00:00:00'),
(9, 5, '2020-01-02 00:00:00'),
(10, 5, '2020-01-03 00:00:00'),
(11, 5, '2020-01-03 00:00:00'),
(12, 3, '2020-01-03 00:00:00'),
(13, 2, '2020-01-04 00:00:00'),
(14, 1, '2020-01-04 00:00:00'),
(15, 5, '2020-01-04 00:00:00'),
(16, 5, '2020-01-04 00:00:00'),
(17, 3, '2020-01-05 00:00:00'),
(18, 1, '2020-01-06 00:00:00'),
(19, 1, '2020-01-06 00:00:00'),
(20, 6, '2020-01-07 00:00:00'),
(21, 6, '2020-01-08 00:00:00'),
(22, 5, '2020-01-10 00:00:00'),
(23, 5, '2020-01-11 00:00:00'),
(24, 5, '2020-01-11 00:00:00'),
(25, 3, '2020-01-13 00:00:00'),
(26, 2, '2020-01-13 00:00:00'),
(27, 7, '2020-01-15 00:00:00'),
(28, 2, '2020-01-16 00:00:00'),
(29, 3, '2020-01-16 00:00:00'),
(30, 4, '2020-01-16 00:00:00'),
(31, 7, '2020-01-18 00:00:00'),
(32, 7, '2020-01-18 00:00:00'),
(33, 7, '2020-01-20 00:00:00'),
(34, 6, '2020-01-21 00:00:00'),
(35, 7, '2020-01-21 00:00:00'),
(36, 6, '2020-01-21 00:00:00'),
(37, 6, '2020-01-22 00:00:00'),
(38, 5, '2020-01-23 00:00:00'),
(39, 5, '2020-01-24 00:00:00'),
(40, 2, '2020-01-25 00:00:00'),
(41, 3, '2020-01-25 00:00:00'),
(42, 4, '2020-01-26 00:00:00'),
(43, 1, '2020-01-26 00:00:00'),
(44, 2, '2020-01-26 00:00:00'),
(45, 3, '2020-01-28 00:00:00'),
(46, 7, '2020-01-28 00:00:00'),
(47, 7, '2020-01-29 00:00:00'),
(48, 7, '2020-01-29 00:00:00'),
(49, 6, '2020-01-29 00:00:00'),
(50, 7, '2020-01-29 00:00:00'),
(51, 6, '2020-01-29 00:00:00'),
(52, 6, '2020-01-29 00:00:00'),
(53, 5, '2020-01-29 00:00:00'),
(54, 5, '2020-01-29 00:00:00'),
(55, 5, '2020-01-29 00:00:00'),
(56, 3, '2020-02-01 00:00:00'),
(57, 2, '2020-02-01 00:00:00'),
(58, 1, '2020-02-01 00:00:00'),
(59, 5, '2020-02-01 00:00:00'),
(60, 3, '2020-02-02 00:00:00'),
(61, 2, '2020-02-02 00:00:00'),
(62, 1, '2020-02-02 00:00:00'),
(63, 2, '2020-02-02 00:00:00'),
(64, 3, '2020-02-02 00:00:00'),
(65, 4, '2020-02-03 00:00:00'),
(66, 2, '2020-02-03 00:00:00'),
(67, 2, '2020-02-03 00:00:00'),
(68, 5, '2020-02-05 00:00:00'),
(69, 5, '2020-02-05 00:00:00'),
(70, 5, '2020-02-05 00:00:00'),
(71, 5, '2020-02-06 00:00:00'),
(72, 7, '2020-02-06 00:00:00'),
(73, 7, '2020-02-07 00:00:00'),
(74, 7, '2020-02-08 00:00:00'),
(75, 6, '2020-02-09 00:00:00'),
(76, 7, '2020-02-09 00:00:00'),
(77, 6, '2020-02-12 00:00:00'),
(78, 6, '2020-02-12 00:00:00'),
(79, 5, '2020-02-12 00:00:00'),
(80, 5, '2020-02-16 00:00:00'),
(81, 5, '2020-02-16 00:00:00'),
(82, 3, '2020-02-18 00:00:00'),
(83, 2, '2020-02-18 00:00:00'),
(84, 1, '2020-02-20 00:00:00'),
(85, 2, '2020-02-20 00:00:00'),
(86, 3, '2020-02-21 00:00:00'),
(87, 4, '2020-02-21 00:00:00');


INSERT INTO `users` (`user_id`, `login`, `password`, `folder_id`, `last_login`, `status`) VALUES
(1, 'user1@example.com', '1111', 'A001', NULL, '1'),
(2, 'user2@example.com', '1111', 'A002', NULL, '1'),
(3, 'user3@example.com', '1111', 'A003', NULL, '1'),
(4, 'user4@example.com', '1111', 'A004', NULL, '1'),
(5, 'user5@example.com', '1111', 'A005', NULL, '1'),
(6, 'user6@example.com', '1111', 'A006', NULL, '1'),
(7, 'user7@example.com', '1111', 'A007', NULL, '1'),
(8, 'user8@example.com', '1111', 'A008', NULL, '1'),
(9, 'user9@example.com', '1111', 'A009', NULL, '1'),
(10, 'user10@example.com', '1111', 'A010', NULL, '1');


INSERT INTO `wallpapers` (`wall_id`, `user_id`, `filename`, `upload_date`, `status`) VALUES
(1, 2, 'wallpaper1.jpg', '2020-02-01 00:00:00', '1'),
(2, 1, 'wallpaper2.jpg', '2020-02-01 00:00:00', '1'),
(3, 1, 'wallpaper3.jpg', '2020-02-01 00:00:00', '1'),
(4, 2, 'wallpaper4.jpg', '2020-02-01 00:00:00', '1'),
(5, 3, 'wallpaper5.jpg', '2020-02-01 00:00:00', '1'),
(6, 5, 'wallpaper6.jpg', '2020-02-08 00:00:00', '1'),
(7, 6, 'wallpaper7.jpg', '2020-02-08 00:00:00', '1'),
(8, 5, 'wallpaper8.jpg', '2020-02-08 00:00:00', '1'),
(9, 6, 'wallpaper9.jpg', '2020-02-08 00:00:00', '1'),
(10, 4, 'wallpaper10.jpg', '2020-02-08 00:00:00', '1'),
(11, 6, 'wallpaper11.jpg', '2020-02-09 00:00:00', '1'),
(12, 5, 'wallpaper12.jpg', '2020-02-09 00:00:00', '1'),
(13, 1, 'wallpaper13.jpg', '2020-02-09 00:00:00', '1'),
(14, 4, 'wallpaper14.jpg', '2020-02-10 00:00:00', '1'),
(15, 6, 'wallpaper15.jpg', '2020-02-10 00:00:00', '1'),
(16, 1, 'wallpaper16.jpg', '2020-02-10 00:00:00', '1'),
(17, 2, 'wallpaper17.jpg', '2020-02-13 00:00:00', '1'),
(18, 4, 'wallpaper18.jpg', '2020-02-13 00:00:00', '1'),
(19, 6, 'wallpaper19.jpg', '2020-02-19 00:00:00', '1'),
(20, 1, 'wallpaper20.jpg', '2020-02-19 00:00:00', '1');

【问题讨论】：

    标签： php mysql


    【解决方案1】：

    试试这个查询

    SELECT U.user_id, U.login,N.dload_id,N.filename,N.total_downloads 
FROM `users` U left join 
( 
   SELECT D.wall_id,W.filename,W.user_id,D.dload_id,count(D.wall_id) as total_downloads 
   FROM `downloads` D 
   left join wallpapers W on D.wall_id=W.wall_id 
   where D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00' 
   GROUP BY D.`wall_id`
) N on U.user_id=N.user_id

    这里你需要使用子查询。试试这个查询，希望它能正常工作。

    【讨论】：

      【解决方案2】：

      您的查询顺序有误。由于您从下载开始，您已经过滤掉了没有下载的用户，无论您放置左连接。如果你从用户开始应该没问题。

      SELECT U.user_id, U.login, D.dload_id, W.filename, IFNULL(COUNT(D.dload_id), 0) AS total_downloads

FROM users AS U

LEFT JOIN wallpapers AS W on W.user_id = U.user_id

LEFT JOIN downloads AS D ON W.wall_id = D.wall_id

WHERE D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00'

GROUP BY U.user_id, filename

ORDER BY user_id ASC LIMIT 500

      【讨论】：

        【解决方案3】：

        你可以使用这个查询

        它正在使用子查询来计算 wall_id 的数量

        SELECT 
U.`user_id`
, U.login
,W.filename
 ,D.total_counts
FROM wallpapers AS W LEFT Join (
SELECT Count(*) total_counts, wall_id FROM downloads AS D
WHERE D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00'
GROUP BY wall_id) D ON D.wall_id = W.wall_id RIGHT JOIN users AS U on W.user_id = U.user_id
ORDER BY U.user_id,W.wall_id;

        -- Table structure for table `downloads`
--

DROP TABLE IF EXISTS `downloads`;
CREATE TABLE IF NOT EXISTS `downloads` (
  `dload_id` int(11) NOT NULL AUTO_INCREMENT,
  `wall_id` int(11) NOT NULL,
  `dload_date` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP,
  PRIMARY KEY (`dload_id`)
) ENGINE=MyISAM AUTO_INCREMENT=88 DEFAULT CHARSET=latin1;
        ✓ ✓ 
        -- Table structure for table `users`
--

DROP TABLE IF EXISTS `users`;
CREATE TABLE IF NOT EXISTS `users` (
  `user_id` int(11) NOT NULL AUTO_INCREMENT,
  `login` varchar(45) DEFAULT NULL,
  `password` varchar(45) DEFAULT NULL,
  `folder_id` varchar(45) DEFAULT NULL,
  `last_login` varchar(45) DEFAULT NULL,
  `status` set('0','1') NOT NULL DEFAULT '1',
  PRIMARY KEY (`user_id`),
  UNIQUE KEY `folder_id_UNIQUE` (`folder_id`),
  UNIQUE KEY `login_UNIQUE` (`login`)
) ENGINE=MyISAM AUTO_INCREMENT=11 DEFAULT CHARSET=latin1;
        ✓ ✓ 
        --

--
-- Table structure for table `wallpapers`
--

DROP TABLE IF EXISTS `wallpapers`;
CREATE TABLE IF NOT EXISTS `wallpapers` (
  `wall_id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) NOT NULL,
  `filename` varchar(100) DEFAULT NULL,
  `upload_date` datetime DEFAULT CURRENT_TIMESTAMP,
  `status` set('0','1') DEFAULT '',
  PRIMARY KEY (`wall_id`)
) ENGINE=MyISAM AUTO_INCREMENT=21 DEFAULT CHARSET=latin1;
        ✓ ✓ 
        INSERT INTO `downloads` (`dload_id`, `wall_id`, `dload_date`) VALUES
(1, 1, '2020-01-01 00:00:00'),
(2, 7, '2020-01-01 00:00:00'),
(3, 7, '2020-01-01 00:00:00'),
(4, 7, '2020-01-01 00:00:00'),
(5, 6, '2020-01-02 00:00:00'),
(6, 7, '2020-01-02 00:00:00'),
(7, 6, '2020-01-02 00:00:00'),
(8, 6, '2020-01-02 00:00:00'),
(9, 5, '2020-01-02 00:00:00'),
(10, 5, '2020-01-03 00:00:00'),
(11, 5, '2020-01-03 00:00:00'),
(12, 3, '2020-01-03 00:00:00'),
(13, 2, '2020-01-04 00:00:00'),
(14, 1, '2020-01-04 00:00:00'),
(15, 5, '2020-01-04 00:00:00'),
(16, 5, '2020-01-04 00:00:00'),
(17, 3, '2020-01-05 00:00:00'),
(18, 1, '2020-01-06 00:00:00'),
(19, 1, '2020-01-06 00:00:00'),
(20, 6, '2020-01-07 00:00:00'),
(21, 6, '2020-01-08 00:00:00'),
(22, 5, '2020-01-10 00:00:00'),
(23, 5, '2020-01-11 00:00:00'),
(24, 5, '2020-01-11 00:00:00'),
(25, 3, '2020-01-13 00:00:00'),
(26, 2, '2020-01-13 00:00:00'),
(27, 7, '2020-01-15 00:00:00'),
(28, 2, '2020-01-16 00:00:00'),
(29, 3, '2020-01-16 00:00:00'),
(30, 4, '2020-01-16 00:00:00'),
(31, 7, '2020-01-18 00:00:00'),
(32, 7, '2020-01-18 00:00:00'),
(33, 7, '2020-01-20 00:00:00'),
(34, 6, '2020-01-21 00:00:00'),
(35, 7, '2020-01-21 00:00:00'),
(36, 6, '2020-01-21 00:00:00'),
(37, 6, '2020-01-22 00:00:00'),
(38, 5, '2020-01-23 00:00:00'),
(39, 5, '2020-01-24 00:00:00'),
(40, 2, '2020-01-25 00:00:00'),
(41, 3, '2020-01-25 00:00:00'),
(42, 4, '2020-01-26 00:00:00'),
(43, 1, '2020-01-26 00:00:00'),
(44, 2, '2020-01-26 00:00:00'),
(45, 3, '2020-01-28 00:00:00'),
(46, 7, '2020-01-28 00:00:00'),
(47, 7, '2020-01-29 00:00:00'),
(48, 7, '2020-01-29 00:00:00'),
(49, 6, '2020-01-29 00:00:00'),
(50, 7, '2020-01-29 00:00:00'),
(51, 6, '2020-01-29 00:00:00'),
(52, 6, '2020-01-29 00:00:00'),
(53, 5, '2020-01-29 00:00:00'),
(54, 5, '2020-01-29 00:00:00'),
(55, 5, '2020-01-29 00:00:00'),
(56, 3, '2020-02-01 00:00:00'),
(57, 2, '2020-02-01 00:00:00'),
(58, 1, '2020-02-01 00:00:00'),
(59, 5, '2020-02-01 00:00:00'),
(60, 3, '2020-02-02 00:00:00'),
(61, 2, '2020-02-02 00:00:00'),
(62, 1, '2020-02-02 00:00:00'),
(63, 2, '2020-02-02 00:00:00'),
(64, 3, '2020-02-02 00:00:00'),
(65, 4, '2020-02-03 00:00:00'),
(66, 2, '2020-02-03 00:00:00'),
(67, 2, '2020-02-03 00:00:00'),
(68, 5, '2020-02-05 00:00:00'),
(69, 5, '2020-02-05 00:00:00'),
(70, 5, '2020-02-05 00:00:00'),
(71, 5, '2020-02-06 00:00:00'),
(72, 7, '2020-02-06 00:00:00'),
(73, 7, '2020-02-07 00:00:00'),
(74, 7, '2020-02-08 00:00:00'),
(75, 6, '2020-02-09 00:00:00'),
(76, 7, '2020-02-09 00:00:00'),
(77, 6, '2020-02-12 00:00:00'),
(78, 6, '2020-02-12 00:00:00'),
(79, 5, '2020-02-12 00:00:00'),
(80, 5, '2020-02-16 00:00:00'),
(81, 5, '2020-02-16 00:00:00'),
(82, 3, '2020-02-18 00:00:00'),
(83, 2, '2020-02-18 00:00:00'),
(84, 1, '2020-02-20 00:00:00'),
(85, 2, '2020-02-20 00:00:00'),
(86, 3, '2020-02-21 00:00:00'),
(87, 4, '2020-02-21 00:00:00');


INSERT INTO `users` (`user_id`, `login`, `password`, `folder_id`, `last_login`, `status`) VALUES
(1, 'user1@example.com', '1111', 'A001', NULL, '1'),
(2, 'user2@example.com', '1111', 'A002', NULL, '1'),
(3, 'user3@example.com', '1111', 'A003', NULL, '1'),
(4, 'user4@example.com', '1111', 'A004', NULL, '1'),
(5, 'user5@example.com', '1111', 'A005', NULL, '1'),
(6, 'user6@example.com', '1111', 'A006', NULL, '1'),
(7, 'user7@example.com', '1111', 'A007', NULL, '1'),
(8, 'user8@example.com', '1111', 'A008', NULL, '1'),
(9, 'user9@example.com', '1111', 'A009', NULL, '1'),
(10, 'user10@example.com', '1111', 'A010', NULL, '1');


INSERT INTO `wallpapers` (`wall_id`, `user_id`, `filename`, `upload_date`, `status`) VALUES
(1, 2, 'wallpaper1.jpg', '2020-02-01 00:00:00', '1'),
(2, 1, 'wallpaper2.jpg', '2020-02-01 00:00:00', '1'),
(3, 1, 'wallpaper3.jpg', '2020-02-01 00:00:00', '1'),
(4, 2, 'wallpaper4.jpg', '2020-02-01 00:00:00', '1'),
(5, 3, 'wallpaper5.jpg', '2020-02-01 00:00:00', '1'),
(6, 5, 'wallpaper6.jpg', '2020-02-08 00:00:00', '1'),
(7, 6, 'wallpaper7.jpg', '2020-02-08 00:00:00', '1'),
(8, 5, 'wallpaper8.jpg', '2020-02-08 00:00:00', '1'),
(9, 6, 'wallpaper9.jpg', '2020-02-08 00:00:00', '1'),
(10, 4, 'wallpaper10.jpg', '2020-02-08 00:00:00', '1'),
(11, 6, 'wallpaper11.jpg', '2020-02-09 00:00:00', '1'),
(12, 5, 'wallpaper12.jpg', '2020-02-09 00:00:00', '1'),
(13, 1, 'wallpaper13.jpg', '2020-02-09 00:00:00', '1'),
(14, 4, 'wallpaper14.jpg', '2020-02-10 00:00:00', '1'),
(15, 6, 'wallpaper15.jpg', '2020-02-10 00:00:00', '1'),
(16, 1, 'wallpaper16.jpg', '2020-02-10 00:00:00', '1'),
(17, 2, 'wallpaper17.jpg', '2020-02-13 00:00:00', '1'),
(18, 4, 'wallpaper18.jpg', '2020-02-13 00:00:00', '1'),
(19, 6, 'wallpaper19.jpg', '2020-02-19 00:00:00', '1'),
(20, 1, 'wallpaper20.jpg', '2020-02-19 00:00:00', '1');
        ✓ ✓ ✓ 
        SELECT 
U.`user_id`
, U.login
,W.filename
 ,D.total_counts
FROM wallpapers AS W LEFT Join (
SELECT Count(*) total_counts, wall_id FROM downloads AS D
WHERE D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00'
GROUP BY wall_id) D ON D.wall_id = W.wall_id RIGHT JOIN users AS U on W.user_id = U.user_id
ORDER BY U.user_id,W.wall_id;
        用户 ID |登录 |文件名 | total_counts ------: | :----------------- | :---------------- | ------------: 1 | user1@example.com |壁纸2.jpg | 5 1 | user1@example.com |壁纸3.jpg | 6 1 | user1@example.com |壁纸13.jpg | 空 1 | user1@example.com |壁纸16.jpg | 空 1 | user1@example.com |壁纸20.jpg | 空 2 | user2@example.com |壁纸1.jpg | 5 2 | user2@example.com |壁纸4.jpg | 2 2 | user2@example.com |壁纸17.jpg | 空 3 | user3@example.com |壁纸5.jpg | 13 4 | user4@example.com |壁纸10.jpg | 空 4 | user4@example.com |壁纸14.jpg | 空 4 | user4@example.com |壁纸18.jpg | 空 5 | user5@example.com |壁纸6.jpg | 11 5 | user5@example.com |壁纸8.jpg | 空 5 | user5@example.com |壁纸12.jpg | 空 6 | user6@example.com |壁纸7.jpg | 13 6 | user6@example.com |壁纸9.jpg | 空 6 | user6@example.com |壁纸11.jpg | 空 6 | user6@example.com |壁纸15.jpg | 空 6 | user6@example.com |壁纸19.jpg | 空 7 | user7@example.com | 空 | 空 8 | user8@example.com | 空 | 空 9 | user9@example.com | 空 | 空 10 | user10@example.com | 空 | 空 
            SELECT U.user_id, U.login, D.dload_id, W.filename, IFNULL(COUNT(D.dload_id), 0) AS total_downloads

    FROM downloads AS D

    LEFT JOIN wallpapers AS W ON W.wall_id = D.wall_id

    LEFT JOIN users AS U on W.user_id = U.user_id

    WHERE D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00'

    GROUP BY U.user_id, U.login, D.dload_id, W.filename

    ORDER BY user_id ASC LIMIT 500
        用户 ID |登录 | dload_id |文件名 | total_downloads ------: | :---------------- | --------: | :------------- | --------------: 1 | user1@example.com | 12 |壁纸3.jpg | 1 1 | user1@example.com | 13 |壁纸2.jpg | 1 1 | user1@example.com | 17 |壁纸3.jpg | 1 1 | user1@example.com | 25 |壁纸3.jpg | 1 1 | user1@example.com | 26 |壁纸2.jpg | 1 1 | user1@example.com | 28 |壁纸2.jpg | 1 1 | user1@example.com | 29 |壁纸3.jpg | 1 1 | user1@example.com | 40 |壁纸2.jpg | 1 1 | user1@example.com | 41 |壁纸3.jpg | 1 1 | user1@example.com | 44 |壁纸2.jpg | 1 1 | user1@example.com | 45 |壁纸3.jpg | 1 2 | user2@example.com | 1 |壁纸1.jpg | 1 2 | user2@example.com | 14 |壁纸1.jpg | 1 2 | user2@example.com | 18 |壁纸1.jpg | 1 2 | user2@example.com | 19 |壁纸1.jpg | 1 2 | user2@example.com | 30 |壁纸4.jpg | 1 2 | user2@example.com | 42 |壁纸4.jpg | 1 2 | user2@example.com | 43 |壁纸1.jpg | 1 3 | user3@example.com | 9 |壁纸5.jpg | 1 3 | user3@example.com | 10 |壁纸5.jpg | 1 3 | user3@example.com | 11 |壁纸5.jpg | 1 3 | user3@example.com | 15 |壁纸5.jpg | 1 3 | user3@example.com | 16 |壁纸5.jpg | 1 3 | user3@example.com | 22 |壁纸5.jpg | 1 3 | user3@example.com | 23 |壁纸5.jpg | 1 3 | user3@example.com | 24 |壁纸5.jpg | 1 3 | user3@example.com | 38 |壁纸5.jpg | 1 3 | user3@example.com | 39 |壁纸5.jpg | 1 3 | user3@example.com | 53 |壁纸5.jpg | 1 3 | user3@example.com | 54 |壁纸5.jpg | 1 3 | user3@example.com | 55 |壁纸5.jpg | 1 5 | user5@example.com | 5 |壁纸6.jpg | 1 5 | user5@example.com | 7 |壁纸6.jpg | 1 5 | user5@example.com | 8 |壁纸6.jpg | 1 5 | user5@example.com | 20 |壁纸6.jpg | 1 5 | user5@example.com | 21 |壁纸6.jpg | 1 5 | user5@example.com | 34 |壁纸6.jpg | 1 5 | user5@example.com | 36 |壁纸6.jpg | 1 5 | user5@example.com | 37 |壁纸6.jpg | 1 5 | user5@example.com | 49 |壁纸6.jpg | 1 5 | user5@example.com | 51 |壁纸6.jpg | 1 5 | user5@example.com | 52 |壁纸6.jpg | 1 6 | user6@example.com | 2 |壁纸7.jpg | 1 6 | user6@example.com | 3 |壁纸7.jpg | 1 6 | user6@example.com | 4 |壁纸7.jpg | 1 6 | user6@example.com | 6 |壁纸7.jpg | 1 6 | user6@example.com | 27 |壁纸7.jpg | 1 6 | user6@example.com | 31 |壁纸7.jpg | 1 6 | user6@example.com | 32 |壁纸7.jpg | 1 6 | user6@example.com | 33 |壁纸7.jpg | 1 6 | user6@example.com | 35 |壁纸7.jpg | 1 6 | user6@example.com | 46 |壁纸7.jpg | 1 6 | user6@example.com | 47 |壁纸7.jpg | 1 6 | user6@example.com | 48 |壁纸7.jpg | 1 6 | user6@example.com | 50 |壁纸7.jpg | 1

        db小提琴here

        【讨论】：

          【解决方案4】：

          如果您希望所有用户都出现在结果中，那么您应该从 Users 开始加入，然后离开加入其他表。
          此外，日期条件应移至ON 子句：

          SELECT U.user_id, U.login, W.filename, 
       COUNT(D.dload_id) AS total_downloads
FROM users AS U
LEFT JOIN wallpapers AS W ON W.user_id = U.user_id
LEFT JOIN downloads AS D ON W.wall_id = D.wall_id 
                        AND D.dload_date BETWEEN '2020-01-01 00:00:00' AND '2020-01-31 00:00:00'
GROUP BY U.user_id, U.login, W.filename
ORDER BY U.user_id ASC LIMIT 500

          不需要IFNULL()，因为如果没有下载，COUNT(D.dload_id) 将返回0。 请参阅demo。

          【讨论】：

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