如何从多个链接表中选择三个外键？图中的图片

Question

嘿伙计们我想学习如何从多个数据库查询到多个数据库。这是一个包含三个表和一个多个表和三个外键的数据库的示例。 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， 它与'st_glowne'表中名称列的特定值相关联， 和'st_pages'表中名称列的specyfic值。 提前致谢！。

TABLE1

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

TABLE2

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？很多人感谢！

Answer 1

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，我建议您重新考虑您的架构 - 是否有任何理由让PK成为名称字段？您有一个AUTO INCREMENT id列，这是一种更加标准的方式来连接两个表。

例如（对于每个表格）：

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,
)