mysql - 动态外键 - 如何实现？

Question

I have 4 tables (appointed, class, elected, status) that I want to cross reference into a single table's (members) column. 4 个表的值是基于历史表 (members_history) 的时间敏感的。所需结果是查询应输出所有成员和当前指定的位置或当前选举位置，类和状态，并包括从外来行获得的其他信息。

因此，不仅仅是返回：

id、用户名、密码、salt、name_first、name_last、date_join & date_leave；

查询将返回

id, 用户名, 密码, salt, name_prefix, name_first, name_last, hours_extra, date_join, date_leave, appointed, class, elected& status;

无论添加的列在历史记录中没有当前值，它的结果都应该为 NULL。

现在我想我可以用子查询来做到这一点，但到目前为止我的头一直在敲击键盘。稍后我会再试一次，但在那之前，还有其他人愿意试一试，或者试图为我指明正确的方向吗？

我的 SQL（没有双关语）表的结构如下：

CREATE TABLE IF NOT EXISTS `members` (
 `id` mediumint(3) unsigned NOT NULL auto_increment COMMENT 'Members Unique Id',
 `username` varchar(32) collate utf8_bin NOT NULL COMMENT 'Mebers Username',
 `password` varchar(64) collate utf8_bin NOT NULL COMMENT 'Members Password Hash',
 `salt` varchar(32) collate utf8_bin NOT NULL COMMENT 'Members Password Salt',
 `name_first` varchar(32) collate utf8_bin NOT NULL COMMENT 'Members First Name',
 `name_last` varchar(32) collate utf8_bin NOT NULL COMMENT 'Members Last Name',
 `date_join` date NOT NULL COMMENT 'Members Join Date',
 `date_leave` date default NULL COMMENT 'Members Resgination Date (If Applicable)',
 PRIMARY KEY  (`id`),
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Members id in this table = mid in other tables';

CREATE TABLE IF NOT EXISTS `members:apointed` (
 `id` tinyint(3) unsigned NOT NULL auto_increment COMMENT 'Unique value',
 `name_prefix` varchar(8) collate utf8_bin NOT NULL COMMENT 'Prefix Added to Members Name',
 `hours_extra` decimal(4,2) NOT NULL COMMENT 'Hours Given as Bonus for Holding this Position.',
 `position` varchar(40) collate utf8_bin NOT NULL COMMENT 'Name of the Posisiton',
 PRIMARY KEY  (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Undefined within the SOP or By-Laws.';

CREATE TABLE IF NOT EXISTS `members:class` (
 `id` tinyint(3) unsigned NOT NULL auto_increment COMMENT 'Unique Id',
 `class` varchar(8) collate utf8_bin NOT NULL COMMENT 'Unique Value',
 PRIMARY KEY  (`id`),
 UNIQUE KEY `value` (`class`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Article I, Section 1 Subsection B: Classes of Membership';

CREATE TABLE IF NOT EXISTS `members:elected` (
 `id` tinyint(3) unsigned NOT NULL auto_increment COMMENT 'Unique value',
 `name_prefix` varchar(8) collate utf8_bin NOT NULL COMMENT 'Prefix Added to Members Name',
 `hours_extra` decimal(4,2) NOT NULL COMMENT 'Hours Given as Bonus for Holding this Position.',
 `position` varchar(40) collate utf8_bin NOT NULL COMMENT 'Name of the Posisiton',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Article II';

CREATE TABLE IF NOT EXISTS `members:status` (
 `id` tinyint(3) unsigned NOT NULL auto_increment COMMENT 'Bit''s Place',
 `status` varchar(16) collate utf8_bin NOT NULL COMMENT 'Categorie''s Name',
 PRIMARY KEY  (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Article I, Section 1, Subsection A: Categories of Membership';

CREATE TABLE IF NOT EXISTS `members_history` (
 `id` int(10) unsigned NOT NULL auto_increment COMMENT 'Unique Id',
 `mid` tinyint(3) unsigned NOT NULL COMMENT 'Members Unique Id.',
 `table` enum('class','elected','appointed','status') NOT NULL COMMENT 'Name of Table that was Edited.',
 `value` tinyint(3) unsigned NOT NULL COMMENT 'Value',
 `start` date NOT NULL COMMENT 'Value''s Effect Date',
 `end` date default NULL COMMENT 'Value''s Expiration Date',
 PRIMARY KEY  (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 COMMENT='Member History';

members_history.mid 是 members 表中 id 的 FK，并非每个成员都有历史记录（但最终他们都会有，因为每个成员都必须有一个类和状态）。members_history.value是一个 FK members:{members_history.table}.id;

INSERT INTO `members`
(`id`, `username`, `password`, `salt`, `name_first`, `name_last`, `date_join`, `date_join`) VALUES
(   1,   'Dygear',MD5('pass'), 's417',       'Mark',    'Tomlin',      DATE(), NULL),
(   2,  'uberusr',MD5('p455'), '235f',     'Howard',    'Singer',      DATE(), NULL),
(   3,'kingchief',MD5('leet'), '32fs','Christopher',   'Buckham',      DATE(), NULL);

INSERT INTO `members:apointed`
(`id`, `name_prefix`, `hours_extra`, `posisiton`) VALUES
(   1,            '',          0.00, 'Crew Chief'),
(   2,            '',         20.00, 'Engineer'),
(   3,         'Lt.',         40.00, 'Lieutenant'),
(   4,       'Capt.',         60.00, 'Captin'),
(   5,      'Chief.',         80.00, '3rd Assistant Chief of Operation');

INSERT INTO `members:class`
(`id`, `class`) VALUES
(   1, 'Class I'),
(   2, 'Class II');

INSERT INTO `members:elected`
(`id`, `name_prefix`, `hours_extra`, `posisiton`) VALUES
(   1,            '',         40.00, 'Trustee'),
(   2,            '',         40.00, 'Chairman of the Board'),
(   3,       'Prez.',         40.00, 'President'),
(   4,      'VPrez.',         40.00, 'Vice-President'),
(   5,            '',         40.00, 'Recording Secretary'),
(   6,            '',         40.00, 'Service Secretary'),
(   7,            '',         40.00, 'Corresponding Secretary'),
(   8,            '',         40.00, 'Financial Secretary Treasuer'),
(   9,            '',         40.00, 'Assistant Financial Secretary Treasuer'),
(  10,      'Chief.',         80.00, 'Chief of Operations'),
(  11,      'Chief.',         80.00, 'First Deputy Chief of Operations'),
(  12,      'Chief.',         80.00, 'Second Deputy Chief of Operation');

INSERT INTO `members:status`
(`id`, `status`) VALUES
(   1, 'Active'),
(   2, 'Inactive'),
(   3, 'Student'),
(   4, 'Probationary'),
(   5, 'Lifetime'),
(   6, 'Cadet'),
(   7, 'Honorary'),
(   8, 'Medical'),
(   9, 'Military'),
(  10, 'Resigned'),
(  11, 'Disvowed');


INSERT INTO `members_history`
(`id`, `mid`,    `table`, `value`, `start`, `end`) VALUES
(NULL,     1, 'apointed',       3,  DATE(), NULL),
(NULL,     1,    'class',       1,  DATE(), NULL),
(NULL,     1,   'status',       1,  DATE(), NULL),
(NULL,     2,  'elected',       4,  DATE(), NULL),
(NULL,     2,    'class',       1,  DATE(), NULL),
(NULL,     2,   'status',       1,  DATE(), NULL),
(NULL,     3, 'apointed',      10,  DATE(), '2010-05-01'),
(NULL,     3,    'class',       1,  DATE(), NULL),
(NULL,     3,   'status',       1,  DATE(), NULL);

Answer 1

您正在使用一种称为多态关联的设计，并且经常出错。使其工作的方法是创建另一个表，例如members:abstract：

CREATE TABLE IF NOT EXISTS `members:abstract` (
 `id` INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
 `type` enum('class','elected','appointed','status') NOT NULL,
  UNIQUE KEY (`id`, `type`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

此表用作所有成员属性表的父表。这些表中的每一个都将其主键更改为不自动生成 id 值，而是引用members:abstract. 我会展示，members:appointed但其他人会相似。

CREATE TABLE IF NOT EXISTS `members:appointed` (
 `id` INT UNSIGNED NOT NULL PRIMARY KEY, -- not auto_increment
 `name_prefix` varchar(8) collate utf8_bin NOT NULL COMMENT 'Prefix Added to Members Name',
 `hours_extra` decimal(4,2) NOT NULL COMMENT 'Hours Given as Bonus for Holding this Position.',
 `position` varchar(40) collate utf8_bin NOT NULL COMMENT 'Name of the Posisiton',
 FOREIGN KEY (`id`) REFERENCES `members:abstract` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Undefined within the SOP or By-Laws.';

您可以使用触发器使此表自动获得自动生成的值：

DELIMITER //
DROP TRIGGER IF EXISTS ins_appointed//
CREATE TRIGGER ins_appointed BEFORE INSERT ON `members:appointed`
FOR EACH ROW BEGIN
  INSERT INTO `members:abstract` (`type`) VALUES ('appointed');
  SET NEW.id = LAST_INSERT_ID();
END; //
DELIMITER ;

对其他每个属性表执行相同的操作。

请注意，id 值现在在所有属性表中都是唯一的。

接下来，您members:abstract将目标设置为 in 中的外键members_history。

CREATE TABLE IF NOT EXISTS `members_history` (
 `id` INT unsigned NOT NULL auto_increment COMMENT 'Unique Id',
 `mid` INT unsigned NOT NULL COMMENT 'Members Unique Id.',
 `value` INT UNSIGNED NOT NULL,
 `table` enum('class','elected','appointed','status') NOT NULL,
 `start` date NOT NULL COMMENT 'Value''s Effect Date',
 `end` date default NULL COMMENT 'Value''s Expiration Date',
 PRIMARY KEY (`id`),
 FOREIGN KEY (`mid`) REFERENCES `members` (`id`) ON DELETE CASCADE,
 FOREIGN KEY (`value`, `table`) REFERENCES `members:abstract` (`id`, `type`) ON DELETE CASCADE
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 COMMENT='Member History';

请注意，该表定义了一个外键，因此您不能在members:abstract.

现在您可以依赖引用完整性和一致性，当您尝试在没有所有引用属性表的公共父级的情况下实现多态关联时，这是不可能的。

这是返回您描述的结果的查询（在 MySQL 5.1.40 上测试）：

SELECT m.username,
  m.password, m.salt, m.name_first, m.name_last,
  MAX(a.name_prefix) AS name_prefix,
  COALESCE(MAX(a.hours_extra), MAX(e.hours_extra)) AS hours_extra,
  MAX(m.date_join) AS date_join,
  MAX(m.date_leave) AS date_leave,
  MAX(a.position) AS appointed,
  MAX(c.class) AS class,
  MAX(e.position) AS elected,
  MAX(s.status) AS status
FROM `members` m 
JOIN `members_history` h ON (h.mid = m.id)
LEFT OUTER JOIN `members:appointed` a ON (h.table = 'appointed' AND h.value = a.id)
LEFT OUTER JOIN `members:class` c ON (h.table = 'class' AND h.value = c.id)
LEFT OUTER JOIN `members:elected` e ON (h.table = 'elected' AND h.value = e.id)
LEFT OUTER JOIN `members:status` s ON (h.table = 'status' AND h.value = s.id)
GROUP BY m.id;

Answer 2

您所需要的只是每个历史记录类型的左外连接以及选择“当前”行所需的任何逻辑。

你的表格结构对我来说没有足够的意义来为你整理一个样本。也许如果您为 ONE 属性提供一个示例成员和几行历史记录，我可以帮助您。