MySQL/Mariadb 问题 : `Order by DESC` before `Group by`-6ren

MySQL/Mariadb 问题 : `Order by DESC` before `Group by`

转载作者：行者123 更新时间：2023-12-04 17:12:44

总结:我想在 Group 之前 Order by

我找到了一篇关于这个问题的好文章，但最终没有成功解决它。 https://eddies-shop.medium.com/mysql-when-to-order-before-group-13d54d6c4ebb

我的服务器配置:

服务器类型:MariaDB
服务器版本:10.6.4-MariaDB - Arch Linux

关于查询:我得到了房间和消息的列表，但我只需要每个房间的最新消息。所以我需要按 conversation_id 分组，并按 message_id 或 message_time 排序。

上述查询运行良好但不完整。这样，对于每个房间，我们都有重复的行。

当我尝试取消注释查询中的最后一行时当我尝试应用 GROUP BY main.conversation_id 时。秩序不再，秩序又被打破。

我的查询:

SELECT
  main.*
FROM
(
    SELECT
        sub.*
    FROM
    (
        SELECT
        conversation.id AS conversation_id,
        CONCAT(user2.first_name, " ", user2.last_name) AS conversation_name,
        conversation.is_group AS conversation_isgroup,
        (SELECT user_id FROM conversation_member WHERE conversation_id = conversation.id AND user_id != 1) AS conversation_owner_id,
    
        message.id AS message_id,
        message.type AS message_type,
        message.body AS message_body,
        message.filename AS message_filename,
        message.created_at AS message_time,

        message.user_id AS message_user_id,
        CONCAT(user.first_name, " ", user.last_name) AS message_user_name
    FROM
        conversation
    INNER JOIN
        conversation_member
        ON
            conversation_member.conversation_id = conversation.id
    LEFT JOIN
        message
        ON
            message.conversation_id = conversation.id
    LEFT JOIN
        user
        ON
            user.id = message.user_id
    LEFT JOIN
        user as user2
        ON
            user2.id = conversation.owner2_id
            OR
            user2.id = conversation.owner_id
    WHERE
        user2.id != 1
        AND
        name IS NULL
        AND
        conversation_member.user_id = 1
        AND
        conversation.is_group = 0
    ) AS sub
    ORDER BY
      sub.message_id DESC
) as main
# GROUP BY
# main.conversation_id

如果您需要了解更多关于数据库结构的信息:

--
-- Table structure for table `conversation`
--

CREATE TABLE `conversation` (
  `id` int(50) NOT NULL,
  `name` varchar(50) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `owner_id` int(50) NOT NULL,
  `owner2_id` int(50) DEFAULT NULL,
  `is_group` int(2) NOT NULL,
  `created_at` timestamp NOT NULL DEFAULT current_timestamp(),
  `updated_at` timestamp NULL DEFAULT NULL ON UPDATE current_timestamp()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Dumping data for table `conversation`
--

INSERT INTO `conversation` (`id`, `name`, `owner_id`, `owner2_id`, `is_group`, `created_at`, `updated_at`) VALUES
(7, 'تالار گفتگوی ریاضی', 1, NULL, 1, '2021-09-13 20:33:38', NULL),
(8, NULL, 2, 1, 0, '2021-09-13 20:33:46', '2021-09-14 07:55:44'),
(9, 'گروه ازمایشی', 3, NULL, 1, '2021-09-14 07:45:04', NULL),
(10, 'پروژه ها و ایده ها', 3, NULL, 1, '2021-09-14 07:47:19', NULL),
(11, NULL, 4, 1, 0, '2021-09-14 08:05:11', NULL);

--
-- Table structure for table `conversation_member`
--

CREATE TABLE `conversation_member` (
  `id` int(50) NOT NULL,
  `conversation_id` int(50) NOT NULL,
  `user_id` int(50) NOT NULL,
  `created_at` timestamp NOT NULL DEFAULT current_timestamp()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Dumping data for table `conversation_member`
--

INSERT INTO `conversation_member` (`id`, `conversation_id`, `user_id`, `created_at`) VALUES
(1, 8, 1, '2021-09-14 07:02:18'),
(2, 8, 2, '2021-09-14 07:02:18'),
(3, 7, 1, '2021-09-14 07:02:28'),
(4, 7, 3, '2021-09-14 07:02:28'),
(5, 9, 3, '2021-09-14 07:45:13'),
(7, 10, 4, '2021-09-14 08:02:57'),
(8, 10, 2, '2021-09-14 08:02:57'),
(9, 10, 1, '2021-09-14 08:03:05'),
(10, 11, 4, '2021-09-14 08:05:23'),
(11, 11, 1, '2021-09-14 08:05:23'),
(12, 7, 4, '2021-09-14 09:30:04');

--
-- Table structure for table `message`
--

CREATE TABLE `message` (
  `id` int(50) NOT NULL,
  `conversation_id` int(50) NOT NULL,
  `user_id` int(50) DEFAULT NULL,
  `type` int(2) NOT NULL COMMENT '0=system,1=message,1=file,2=voice',
  `body` text COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `filename` varchar(250) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `is_group` int(2) NOT NULL,
  `created_at` timestamp NOT NULL DEFAULT current_timestamp(),
  `edited_at` timestamp NULL DEFAULT NULL ON UPDATE current_timestamp()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Dumping data for table `message`
--

INSERT INTO `message` (`id`, `conversation_id`, `user_id`, `type`, `body`, `filename`, `is_group`, `created_at`, `edited_at`) VALUES
(1, 7, 1, 1, '1', NULL, 1, '2021-09-14 07:16:12', '2021-09-14 14:14:44'),
(2, 8, 1, 1, '2', NULL, 0, '2021-09-14 07:16:25', '2021-09-14 14:14:45'),
(3, 11, 1, 1, '3', NULL, 0, '2021-09-14 13:21:30', '2021-09-14 14:14:47'),
(4, 10, 1, 1, '4', NULL, 1, '2021-09-14 13:23:34', '2021-09-14 14:14:49'),
(5, 7, 1, 1, '5', NULL, 1, '2021-09-14 13:25:16', '2021-09-14 14:14:51'),
(6, 7, 1, 1, '6', NULL, 1, '2021-09-14 13:30:40', '2021-09-14 14:14:52'),
(7, 7, 1, 1, '7', NULL, 1, '2021-09-14 13:49:29', '2021-09-14 14:14:54'),
(8, 7, 1, 1, '8', NULL, 1, '2021-09-14 13:49:34', '2021-09-14 14:14:56'),
(9, 10, 1, 1, '9', NULL, 1, '2021-09-14 13:54:04', '2021-09-14 14:14:57'),
(10, 7, 1, 1, '10', NULL, 1, '2021-09-14 14:01:18', '2021-09-14 14:14:59'),
(11, 8, 1, 1, '11', NULL, 0, '2021-09-14 14:07:48', '2021-09-14 14:15:03'),
(12, 11, 4, 1, 'test-new', NULL, 0, '2021-09-14 15:11:51', NULL),
(13, 11, 1, 1, 'fdgdfg', NULL, 0, '2021-09-14 13:21:30', '2021-09-14 14:14:47'),
(14, 11, 1, 1, 'sd1f23sd1f', NULL, 0, '2021-09-14 15:33:02', NULL),
(15, 11, 1, 1, 'dfgdfgdfgdfg', NULL, 0, '2021-09-14 15:33:02', NULL),
(16, 11, 1, 1, 'dfgdfgdfg', NULL, 0, '2021-09-14 15:33:06', NULL),
(17, 11, 1, 1, 'dfg345345345', NULL, 0, '2021-09-14 15:33:06', NULL),
(18, 11, 1, 1, 'gdfg234234234', NULL, 0, '2021-09-14 15:33:17', NULL),
(19, 11, 1, 1, 'dfgda1323123f', NULL, 0, '2021-09-14 15:33:17', NULL),
(20, 11, 1, 1, '234234234234', NULL, 0, '2021-09-14 15:33:17', NULL),
(21, 11, 1, 1, '345345345345', NULL, 0, '2021-09-14 15:33:17', NULL),
(22, 11, 1, 1, '5565656', NULL, 0, '2021-09-14 15:33:17', NULL),
(23, 11, 1, 1, '7787878', NULL, 0, '2021-09-14 15:33:17', NULL),
(24, 11, 1, 1, 'یبلیبلیبلیبل', NULL, 0, '2021-09-14 15:33:28', NULL),
(25, 11, 1, 1, 'ض۳۲ث۱۲۳۴۲۳۴۲۳۴', NULL, 0, '2021-09-14 15:33:28', NULL),
(26, 11, 1, 1, '۳۴۵سیبیلبیبلب', NULL, 0, '2021-09-14 15:33:28', NULL),
(27, 11, 1, 1, 'فقفثفثقفثقف', NULL, 0, '2021-09-14 15:33:28', NULL),
(28, 11, 1, 1, '۳۳۴۲۴۲۳۴', NULL, 0, '2021-09-14 15:33:28', NULL),
(29, 11, 1, 1, '$$$$', NULL, 0, '2021-09-14 15:33:28', NULL),
(30, 11, 1, 1, '$$$%%dfgdfg', NULL, 0, '2021-09-14 15:33:47', NULL),
(31, 11, 1, 1, 'dfgdfg23423423423سیبلیبل', NULL, 0, '2021-09-14 15:33:47', NULL),
(32, 11, 1, 1, 'یبلص۴۳۵۲۳۴۵۳۴۵۳۴۵', NULL, 0, '2021-09-14 15:33:47', NULL),
(33, 11, 1, 1, 'یبل۳۵۳۴۵فثقیبلیبلیبل', NULL, 0, '2021-09-14 15:33:47', NULL),
(34, 11, 1, 1, 'یبلیلبل۳۴۵۳۴۵۳۴۵۳۴۵۳۴۵', NULL, 0, '2021-09-14 15:33:47', NULL),
(35, 11, 1, 1, '$$$$$####', NULL, 0, '2021-09-14 15:33:47', NULL);

--
-- Table structure for table `message_view`
--

CREATE TABLE `message_view` (
  `id` int(50) NOT NULL,
  `message_id` int(50) NOT NULL,
  `conversation_id` int(50) NOT NULL,
  `is_group` int(2) NOT NULL,
  `user_id` int(50) NOT NULL,
  `viewed_at` timestamp NOT NULL DEFAULT current_timestamp()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Table structure for table `session`
--

CREATE TABLE `session` (
  `id` int(50) NOT NULL,
  `user_id` int(50) NOT NULL,
  `device` varchar(250) COLLATE utf8mb4_unicode_ci NOT NULL,
  `code` int(10) DEFAULT NULL,
  `secret` varchar(250) COLLATE utf8mb4_unicode_ci DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Dumping data for table `session`
--

INSERT INTO `session` (`id`, `user_id`, `device`, `code`, `secret`) VALUES
(1, 1, '08ad5559-15f7-4c32-ab2d-2d8a563670a3', 0, '1'),
(2, 1, 'c8216675-08ff-4deb-9341-2afbe88bc716', NULL, '41234'),
(3, 1, 'f20279f4-615d-4b6f-83e4-0e6c201395e3', 53741, NULL),
(4, 1, 'bef6f3e2-04b7-4ff5-b948-c035c376f4d2', 51003, NULL),
(5, 1, '3492d860-6ae4-4a00-a65d-346d880c4e71', 30646, NULL),
(6, 1, 'fd0b2d35-d7aa-4e40-b362-6b592dc17aad', 28576, NULL),
(7, 1, 'c69516b4-53a8-4e69-a874-a11d859b451d', 32440, NULL),
(8, 1, '075149a4-d94c-4246-99ce-d0b71c72f26c', 99800, NULL),
(9, 1, '4804b854-89b6-4c85-8df3-815ffdd34fba', 19774, NULL),
(10, 1, 'a60195ac-2e50-42ed-9d71-1d3d04729339', 10262, NULL),
(11, 1, '80a9a2e7-ee8b-47ef-8ca4-75216721a6ac', 88424, 'bc82131e-0e59-4841-98b7-798cf65d9fcb'),
(12, 1, '6c120179-312f-4d73-9488-7f692cb54234', 42832, NULL),
(13, 1, 'a8b7ca5b-a47d-48b0-afeb-197b5ec7dc44', 39034, 'fdd51fe1-5bae-424f-9515-1a1b435faed6'),
(14, 1, '0652aa2a-01df-497d-b7b2-77fc87a29c24', 36133, '8fc206e1-1a49-444b-bcb6-ea289c17a918'),
(15, 1, '6b0bf6b9-4d32-4c6b-9e84-fd0b393acb31', 87972, '05de4b7a-cc6e-4ff0-b321-72473ac903bd'),
(16, 1, '0a523464-89ab-4f4a-803e-ca252e637e4f', 40843, 'a35a2169-949d-4043-a061-1a56ec30440e'),
(17, 1, '34b2e1bf-a088-48e8-85b8-1943db001fd5', 65916, '971a3cea-8ccc-45bf-887e-7797e4c6ab22'),
(18, 1, 'fcdb6c98-d044-43e8-a373-351f7ca1536d', 82257, 'bacb442d-e066-4117-a380-c468316d47f2'),
(19, 1, '565a036d-c4f8-46b0-8493-e5371e3dccca', 71626, '610b4e81-cf72-4091-a711-d64c601e0f0c'),
(20, 1, '8775a2d9-4544-48c4-ab5c-6d7216c955f7', 46912, 'b5eabb83-e372-4e7b-a48a-3c99eaba5d6d'),
(21, 1, 'a94f734b-0aa0-4ee9-aea3-86e2a405cf56', 44508, '2db51630-e32a-4172-90aa-99d5f7b00063'),
(22, 1, 'b0ed316b-483b-47cc-b27f-2fe6b83f410a', 87850, 'f68377a4-3ed8-4c36-8a78-1d807ed50449'),
(23, 1, '08f38458-cd12-4a9c-9c63-9c6aa291956b', 79266, 'e6314070-8401-4d7b-b9d7-a44c147c75ec'),
(24, 4, '192dfd3f-b2d7-401f-bf95-2d663b6badab', 65088, '6fa66aa9-f47d-46fd-9ce5-9645802383da'),
(25, 4, 'fc8fe94b-f220-42db-ab77-74de994f8275', 37715, '0e188502-67c2-44a9-b68c-32b07fa150ab'),
(26, 1, '27451de6-c730-450a-b76c-3ea53ff74580', 16934, '662ae741-fa42-4fc3-b0bb-5ae6c9e67b52'),
(27, 4, '6ba92f55-cffe-4d9e-b646-be9cf07e99e3', 91683, '27b85d09-831d-41cd-8032-17743a76616d');

--
-- Table structure for table `user`
--

CREATE TABLE `user` (
  `id` int(50) NOT NULL,
  `first_name` varchar(40) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `last_name` varchar(40) COLLATE utf8mb4_unicode_ci DEFAULT NULL,
  `country_code` int(2) NOT NULL,
  `phone_number` varchar(13) COLLATE utf8mb4_unicode_ci NOT NULL,
  `created_at` timestamp NOT NULL DEFAULT current_timestamp(),
  `updated_at` timestamp NULL DEFAULT NULL ON UPDATE current_timestamp()
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

--
-- Dumping data for table `user`
--

INSERT INTO `user` (`id`, `first_name`, `last_name`, `country_code`, `phone_number`, `created_at`, `updated_at`) VALUES
(1, 'Max', 'Base', 98, '9134458080', '2021-09-13 18:28:47', '2021-09-14 07:13:21'),
(2, 'Ali', 'Tahmasebi', 98, '91032545254', '2021-09-14 07:02:46', '2021-09-14 08:02:24'),
(3, 'B.', 'KheirKhah', 98, '9124554020', '2021-09-14 07:02:46', '2021-09-14 08:03:20'),
(4, 'H.', 'Malekian', 98, '9134550773', '2021-09-14 07:25:21', '2021-09-14 08:02:35');

--
-- Indexes for dumped tables
--

--
-- Indexes for table `conversation`
--
ALTER TABLE `conversation`
  ADD PRIMARY KEY (`id`),
  ADD KEY `owner_id` (`owner_id`),
  ADD KEY `is_group` (`is_group`);

--
-- Indexes for table `conversation_member`
--
ALTER TABLE `conversation_member`
  ADD PRIMARY KEY (`id`);

--
-- Indexes for table `message`
--
ALTER TABLE `message`
  ADD PRIMARY KEY (`id`),
  ADD KEY `is_group` (`is_group`),
  ADD KEY `user_id` (`user_id`),
  ADD KEY `conversation_id` (`conversation_id`);

--
-- Indexes for table `message_view`
--
ALTER TABLE `message_view`
  ADD PRIMARY KEY (`id`);

--
-- Indexes for table `session`
--
ALTER TABLE `session`
  ADD PRIMARY KEY (`id`),
  ADD KEY `user_id` (`user_id`),
  ADD KEY `device` (`device`);

--
-- Indexes for table `user`
--
ALTER TABLE `user`
  ADD PRIMARY KEY (`id`),
  ADD KEY `phone_number` (`phone_number`),
  ADD KEY `country_code` (`country_code`);

--
-- AUTO_INCREMENT for dumped tables
--

--
-- AUTO_INCREMENT for table `conversation`
--
ALTER TABLE `conversation`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=12;

--
-- AUTO_INCREMENT for table `conversation_member`
--
ALTER TABLE `conversation_member`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=13;

--
-- AUTO_INCREMENT for table `message`
--
ALTER TABLE `message`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=12;

--
-- AUTO_INCREMENT for table `message_view`
--
ALTER TABLE `message_view`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT;

--
-- AUTO_INCREMENT for table `session`
--
ALTER TABLE `session`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=28;

--
-- AUTO_INCREMENT for table `user`
--
ALTER TABLE `user`
  MODIFY `id` int(50) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=5;
COMMIT;

关于数据库和表的更多信息:

conversation，conversation_member 表的目的:我有一个数据库来存储信使数据。有 2 个模型对话:

1:组:多人
2:个人聊天:一个用户与另一个用户(这就是为什么我有 owner2_id 列的原因。)

主要查询是合并 ID = 1 用户的个人聊天和群组聊天:

(
    SELECT
        sub1.*
    FROM
    (
        SELECT
            conversation.id AS conversation_id,
            conversation.name AS conversation_name,
            conversation.is_group AS conversation_isgroup,
            conversation.owner_id AS conversation_owner_id,

            message.id AS message_id,
            message.type AS message_type,
            message.body AS message_body,
            message.filename AS message_filename,
            message.created_at AS message_time,

            message.user_id AS message_user_id,
            CONCAT(user.first_name, " ", user.last_name) AS message_user_name
        FROM
            conversation
        INNER JOIN
            conversation_member
            ON
                conversation_member.conversation_id = conversation.id
        LEFT JOIN
            message
            ON
                message.conversation_id = conversation.id
        LEFT JOIN
            user
            ON
                user.id = message.user_id
        WHERE
            conversation_member.user_id = 1
            AND
            conversation.is_group = 1
    ) AS sub1
    GROUP BY sub1.message_id desc
)
UNION
(
    SELECT
        sub2.*
    FROM
    (
        SELECT
            conversation.id AS conversation_id,
            CONCAT(user2.first_name, " ", user2.last_name) AS conversation_name,
            conversation.is_group AS conversation_isgroup,
            (SELECT user_id FROM conversation_member WHERE conversation_id = conversation.id AND user_id != 1) AS conversation_owner_id,

            message.id AS message_id,
            message.type AS message_type,
            message.body AS message_body,
            message.filename AS message_filename,
            message.created_at AS message_time,

            message.user_id AS message_user_id,
            CONCAT(user.first_name, " ", user.last_name) AS message_user_name
        FROM
            conversation
        INNER JOIN
            conversation_member
            ON
                conversation_member.conversation_id = conversation.id
        LEFT JOIN
            message
            ON
                message.conversation_id = conversation.id
        LEFT JOIN
            user
            ON
                user.id = message.user_id
        LEFT JOIN
            user as user2
            ON
                user2.id = conversation.owner2_id
                OR
                user2.id = conversation.owner_id
        WHERE
            user2.id != 1
            AND
            name IS NULL
            AND
            conversation_member.user_id = 1
            AND
            conversation.is_group = 0
    ) AS sub2
    GROUP BY sub2.message_id desc
);

我在做什么

我想要一个所有群组对话和个人对话的列表以及该房间中的最后消息，并按最后 MESSAGE_TIME 对所有房间进行排序。

几乎所有信使都会遇到这种情况。

最佳答案

我将只使用关于你问题的查询来展示 MariaDB 如何处理子查询中的 order by。

我用 user01 更改了您的 user 表，因为我的 MariaDB 数据库中有一个表 user。

SELECT
  main.*
FROM
(
    SELECT
        sub.*
    FROM
    (
        SELECT
        conversation.id AS conversation_id,
        CONCAT(user2.first_name, " ", user2.last_name) AS conversation_name,
        conversation.is_group AS conversation_isgroup,
        (SELECT user_id FROM conversation_member WHERE conversation_id = conversation.id AND user_id != 1) AS conversation_owner_id,
    
        message.id AS message_id,
        message.type AS message_type,
        message.body AS message_body,
        message.filename AS message_filename,
        message.created_at AS message_time,

        message.user_id AS message_user_id,
        CONCAT(user01.first_name, " ", user01.last_name) AS message_user_name
    FROM
        conversation
    INNER JOIN
        conversation_member
        ON
            conversation_member.conversation_id = conversation.id
    LEFT JOIN
        message
        ON
            message.conversation_id = conversation.id
    LEFT JOIN
        user01
        ON
            user01.id = message.user_id
    LEFT JOIN
        user01 as user2
        ON
            user2.id = conversation.owner2_id
            OR
            user2.id = conversation.owner_id
    WHERE
        user2.id != 1
        AND
        name IS NULL
        AND
        conversation_member.user_id = 1
        AND
        conversation.is_group = 0
    ) AS sub
    ORDER BY
      sub.message_id DESC limit 10 
) as main
 GROUP BY
 main.conversation_id;

我只在 sub.message_id DESC limit 10 上添加了 limit 10。

A "table" (and subquery in the FROM clause too) is - according to theSQL standard - an unordered set of rows. Rows in a table (or in asubquery in the FROM clause) do not come in any specific order. That'swhy the optimizer can ignore the ORDER BY clause that you havespecified. In fact, the SQL standard does not even allow the ORDER BYclause to appear in this subquery (we allow it, because ORDER BY ...LIMIT ... changes the result, the set of rows, not only their order).

You need to treat the subquery in the FROM clause, as a set of rows insome unspecified and undefined order, and put the ORDER BY on thetop-level SELECT

https://mariadb.com/kb/en/why-is-order-by-in-a-from-subquery-ignored/

关于MySQL/Mariadb 问题 : `Order by DESC` before `Group by` ，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/69180293/

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MySQL/Mariadb 问题 : `Order by DESC` before `Group by`

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