mysql - 在 n 个其他表之一中具有单亲的表

Question

假设我有这样一个架构:

group
-----
id

site
----
id
group_id (optional)

person
------
id
group_id (one of these two must exist 
site_id   and the other must be null)

device
------
id 
group_id  (one of these three must exist 
site_id    and the others must be null)
person_id  

我不喜欢这种表现形式，但我正在努力寻找更好的表现形式。

我想到的两种选择是:

device
------
id 
parent_table_name
parent_id

(但这很糟糕，因为我不能再有外键了)

和:

entity
------
id

group
-----
entity_id

site
----
entity_id
link_entity_id (optional)

person
------
entity_id
link_entity_id (optional)

device
------
entity_id
link_entity_id

这也不完美。这实际上是 Django ORMs 的继承方法，其中实体是所有其他类的父类。

是否有更好的数据结构方式，或者 SQL 是否与 DAG 格格不入？

有没有办法向人员和设备表添加CONSTRAINT？

Answer 1

以下 MySQL 结构应该正常化。在某些情况下，它会使您的查询编写起来稍微复杂一些，但它会使应用程序更强大，并且能够在不影响性能的情况下呈指数增长。我们有一个大型 MySQL 数据库，其中包含许多相关表，这些表为人们提供各种采访、笔记和其他非常有用的数据的外键!需要注意的是，如果您使用组作为表名，请记住使用 `` 标记，例如:

`group`

这样 MySQL 就不会尝试使 INNER JOIN group ON (foo=bar) 无效并期望 GROUP BY。您还必须在应用程序的前端设置限制，以防止在没有父设备的情况下添加设备(如果这是所需的目标)。但这并不难做到。无论如何，请查看示例并享受实验/编程的乐趣!

在线演示:http://www.sqlfiddle.com/#!2/e9e94/2/0

这是建议的 MySQL 表结构，其中包含最少的数据，以说明您问题中每个所需案例的一个实例:复制并粘贴到 .sql 文件中，然后使用 phpMyAdmin 导入到空数据库

-- phpMyAdmin SQL Dump
-- version 3.5.2.2
-- http://www.phpmyadmin.net
--
-- Host: 127.0.0.1
-- Generation Time: Jun 07, 2013 at 08:14 PM
-- Server version: 5.5.27
-- PHP Version: 5.4.7

SET FOREIGN_KEY_CHECKS=0;
SET SQL_MODE="NO_AUTO_VALUE_ON_ZERO";
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 utf8 */;

--
-- Database: `stackoverflow`
--

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

--
-- Table structure for table `device`
--

CREATE TABLE IF NOT EXISTS `device` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ;

--
-- Dumping data for table `device`
--

INSERT INTO `device` (`id`) VALUES
(1),
(2),
(3),
(4),
(5),
(6);

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

--
-- Table structure for table `group`
--

CREATE TABLE IF NOT EXISTS `group` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=9 ;

--
-- Dumping data for table `group`
--

INSERT INTO `group` (`id`) VALUES
(1),
(2),
(3),
(4),
(5),
(6),
(7),
(8);

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

--
-- Table structure for table `groups_have_devices`
--

CREATE TABLE IF NOT EXISTS `groups_have_devices` (
  `group_id` int(11) NOT NULL,
  `device_id` int(11) NOT NULL,
  PRIMARY KEY (`group_id`,`device_id`),
  KEY `device_id` (`device_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `groups_have_devices`
--

INSERT INTO `groups_have_devices` (`group_id`, `device_id`) VALUES
(4, 6);

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

--
-- Table structure for table `groups_have_people`
--

CREATE TABLE IF NOT EXISTS `groups_have_people` (
  `group_id` int(11) NOT NULL,
  `person_id` int(11) NOT NULL,
  PRIMARY KEY (`group_id`,`person_id`),
  KEY `person_id` (`person_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `groups_have_people`
--

INSERT INTO `groups_have_people` (`group_id`, `person_id`) VALUES
(1, 2),
(5, 5);

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

--
-- Table structure for table `groups_have_sites`
--

CREATE TABLE IF NOT EXISTS `groups_have_sites` (
  `group_id` int(11) NOT NULL,
  `site_id` int(11) NOT NULL,
  PRIMARY KEY (`group_id`,`site_id`),
  KEY `site_id` (`site_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `groups_have_sites`
--

INSERT INTO `groups_have_sites` (`group_id`, `site_id`) VALUES
(2, 2),
(3, 4),
(6, 6),
(7, 8);

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

--
-- Table structure for table `people_have_devices`
--

CREATE TABLE IF NOT EXISTS `people_have_devices` (
  `person_id` int(11) NOT NULL,
  `device_id` int(11) NOT NULL,
  PRIMARY KEY (`person_id`,`device_id`),
  KEY `device_id` (`device_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `people_have_devices`
--

INSERT INTO `people_have_devices` (`person_id`, `device_id`) VALUES
(1, 1),
(2, 2),
(3, 3);

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

--
-- Table structure for table `person`
--

CREATE TABLE IF NOT EXISTS `person` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=7 ;

--
-- Dumping data for table `person`
--

INSERT INTO `person` (`id`) VALUES
(1),
(2),
(3),
(4),
(5),
(6);

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

--
-- Table structure for table `site`
--

CREATE TABLE IF NOT EXISTS `site` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 AUTO_INCREMENT=9 ;

--
-- Dumping data for table `site`
--

INSERT INTO `site` (`id`) VALUES
(1),
(2),
(3),
(4),
(5),
(6),
(7),
(8);

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

--
-- Table structure for table `sites_have_devices`
--

CREATE TABLE IF NOT EXISTS `sites_have_devices` (
  `site_id` int(11) NOT NULL,
  `device_id` int(11) NOT NULL,
  PRIMARY KEY (`site_id`,`device_id`),
  KEY `device_id` (`device_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `sites_have_devices`
--

INSERT INTO `sites_have_devices` (`site_id`, `device_id`) VALUES
(3, 4),
(4, 5);

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

--
-- Table structure for table `sites_have_people`
--

CREATE TABLE IF NOT EXISTS `sites_have_people` (
  `site_id` int(11) NOT NULL,
  `person_id` int(11) NOT NULL,
  PRIMARY KEY (`site_id`,`person_id`),
  KEY `person_id` (`person_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

--
-- Dumping data for table `sites_have_people`
--

INSERT INTO `sites_have_people` (`site_id`, `person_id`) VALUES
(1, 1),
(2, 3),
(5, 4),
(6, 6);

--
-- Constraints for dumped tables
--

--
-- Constraints for table `groups_have_devices`
--
ALTER TABLE `groups_have_devices`
  ADD CONSTRAINT `groups_have_devices_ibfk_2` FOREIGN KEY (`device_id`) REFERENCES `device` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `groups_have_devices_ibfk_1` FOREIGN KEY (`group_id`) REFERENCES `group` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

--
-- Constraints for table `groups_have_people`
--
ALTER TABLE `groups_have_people`
  ADD CONSTRAINT `groups_have_people_ibfk_2` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `groups_have_people_ibfk_1` FOREIGN KEY (`group_id`) REFERENCES `group` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

--
-- Constraints for table `groups_have_sites`
--
ALTER TABLE `groups_have_sites`
  ADD CONSTRAINT `groups_have_sites_ibfk_2` FOREIGN KEY (`site_id`) REFERENCES `site` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `groups_have_sites_ibfk_1` FOREIGN KEY (`group_id`) REFERENCES `group` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

--
-- Constraints for table `people_have_devices`
--
ALTER TABLE `people_have_devices`
  ADD CONSTRAINT `people_have_devices_ibfk_2` FOREIGN KEY (`device_id`) REFERENCES `device` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `people_have_devices_ibfk_1` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

--
-- Constraints for table `sites_have_devices`
--
ALTER TABLE `sites_have_devices`
  ADD CONSTRAINT `sites_have_devices_ibfk_2` FOREIGN KEY (`device_id`) REFERENCES `device` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `sites_have_devices_ibfk_1` FOREIGN KEY (`site_id`) REFERENCES `site` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;

--
-- Constraints for table `sites_have_people`
--
ALTER TABLE `sites_have_people`
  ADD CONSTRAINT `sites_have_people_ibfk_2` FOREIGN KEY (`person_id`) REFERENCES `person` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
  ADD CONSTRAINT `sites_have_people_ibfk_1` FOREIGN KEY (`site_id`) REFERENCES `site` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION;
SET FOREIGN_KEY_CHECKS=1;

/*!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 */;

这是一个查找每个组的所有子设备的查询。

SELECT
  `group`.`id` AS `group_id`,
  `device`.`id` AS `device_id`
FROM
  `group`
  INNER JOIN groups_have_devices
    ON (group.id=groups_have_devices.group_id)
  INNER JOIN device
    ON (groups_have_devices.device_id=device.id)

UNION ALL

SELECT
  `group`.`id` AS `group_id`,
  `device`.`id` AS `device_id`
FROM
  `group`
  INNER JOIN groups_have_people
    ON (group.id=groups_have_people.group_id)
  INNER JOIN person
    ON (groups_have_people.person_id=person.id)
  INNER JOIN people_have_devices
    ON (person.id=people_have_devices.person_id)
  INNER JOIN device
    ON (people_have_devices.device_id=device.id)

UNION ALL

SELECT
  `group`.`id` AS `group_id`,
  `device`.`id` AS `device_id`
FROM
  `group`
  INNER JOIN groups_have_sites
    ON (group.id=groups_have_sites.group_id)
  INNER JOIN site
    ON (groups_have_sites.site_id=site.id)
  INNER JOIN sites_have_devices
    ON (site.id=sites_have_devices.site_id)
  INNER JOIN device
    ON (sites_have_devices.device_id=device.id)

UNION ALL

SELECT
  `group`.`id` AS `group_id`,
  `device`.`id` AS `device_id`
FROM
  `group`
  INNER JOIN groups_have_sites
    ON (group.id=groups_have_sites.group_id)
  INNER JOIN site
    ON (groups_have_sites.site_id=site.id)
  INNER JOIN sites_have_people
    ON (site.id=sites_have_people.site_id)
  INNER JOIN person
    ON (sites_have_people.person_id=person.id)
  INNER JOIN people_have_devices
    ON (person.id=people_have_devices.person_id)
  INNER JOIN device
    ON (people_have_devices.device_id=device.id)
ORDER BY
  group_id

这里是获取所有设备及其直接父级的查询。

SELECT
  device.id AS device_id,
  person.id AS person_id,
  NULL AS site_id,
  NULL AS group_id
FROM
  device
  INNER JOIN people_have_devices
    ON (device.id=people_have_devices.device_id)
  INNER JOIN person
    ON (people_have_devices.person_id=person.id)

UNION ALL

SELECT
  device.id AS device_id,
  NULL AS person_id,
  site.id AS site_id,
  NULL AS group_id
FROM
  device
  INNER JOIN sites_have_devices
    ON (device.id=sites_have_devices.device_id)
  INNER JOIN site
    ON (sites_have_devices.site_id=site.id)

UNION ALL

SELECT
  device.id AS device_id,
  NULL AS person_id,
  NULL AS site_id,
  group.id AS group_id
FROM
  device
  INNER JOIN groups_have_devices
    ON (device.id=groups_have_devices.device_id)
  INNER JOIN `group`
    ON (groups_have_devices.group_id=group.id)

您可以像这样进一步获取作为特定人员、组或站点的直接子设备

SELECT
  device_id
FROM (
  SELECT
    device.id AS device_id,
    NULL AS person_id,
    site.id AS site_id,
    NULL AS group_id
  FROM
    device
    INNER JOIN sites_have_devices
      ON (device.id=sites_have_devices.device_id)
    INNER JOIN site
      ON (sites_have_devices.site_id=site.id)
) sub_query
WHERE
  sub_query.site_id='3'