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嘿伙计们，我想学习如何从多对多数据库进行查询。这是具有三个表和一个具有三个外键的多对多表的数据库示例。您将如何在st_glowne_others表上执行 SELECT 语句？

例如，如果我想从“st_components”表中选择所有可能的结果，该表与“st_glowne”表中名称列的特定值和“st_pages”表中名称列的特定值链接。提前致谢！。

具有三个外键的多对多

表格1

CREATE TABLE `st_glowne` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `location` varchar(50) COLLATE utf8_polish_ci NOT NULL DEFAULT './',
 PRIMARY KEY (`name`),
 KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COLLATE=utf8_polish_ci

表2

CREATE TABLE `st_pages` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `filelocation` varchar(50) COLLATE utf8_polish_ci NOT NULL DEFAULT 'pages/',
 PRIMARY KEY (`name`),
 KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 COLLATE=utf8_polish_c

表3

CREATE TABLE `st_components` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `location` varchar(100) COLLATE utf8_polish_ci NOT NULL DEFAULT 'components/',
 PRIMARY KEY (`name`),
 KEY `id` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_polish_ci

这是我们要查询的表：

CREATE TABLE `st_glowne_others` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `st_glowne` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `st_pages` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `st_components` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 PRIMARY KEY (`id`),
 KEY `id` (`id`),
 KEY `st_glowne` (`st_glowne`),
 KEY `st_pages` (`st_pages`),
 KEY `st_components` (`st_components`),
 KEY `st_components_2` (`st_components`),
 CONSTRAINT `st_glowne_others_ibfk_3` FOREIGN KEY (`st_components`) REFERENCES `st_components` (`name`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `st_glowne_others_ibfk_1` FOREIGN KEY (`st_glowne`) REFERENCES `st_glowne` (`name`) ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT `st_glowne_others_ibfk_2` FOREIGN KEY (`st_pages`) REFERENCES `st_pages` (`name`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8 COLLATE=utf8_polish_ci

你能告诉我如何从中查询吗？非常感谢 ！

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1 回答 1

2

最简单的方法是加入：

SELECT * FROM `st_glowne_others` go
LEFT JOIN `st_glowne` ON `st_glowne`.name = go.st_glowne
LEFT JOIN `st_pages` ON `st_pages`.name = go.st_pages
LEFT JOIN `st_components` ON `st_components`.name = go.st_components

但是，我建议重新考虑您的架构 - PK 是否有任何理由成为名称字段？您有一个AUTO INCREMENTid 列，这是连接两个表的更标准方法。

例如（对于每个表）：

CREATE TABLE `st_glowne` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `name` varchar(50) COLLATE utf8_polish_ci NOT NULL,
 `location` varchar(50) COLLATE utf8_polish_ci NOT NULL DEFAULT './',
 PRIMARY KEY (`id`),
)

然后使用您的st_glowne_others表，引用 ID 列。

CREATE TABLE `st_glowne_others` (
 `id` int(11) NOT NULL AUTO_INCREMENT,
 `st_glowne_id` int(11) NOT NULL,
 PRIMARY KEY (`id`),
 KEY `st_glowne_id` (`st_glowne_id`),
 CONSTRAINT `st_glowne_others_ibfk_3` FOREIGN KEY (`st_glowne_id`) REFERENCES `st_glowne` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
)
于 2013-09-22T00:54:24.577 回答