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mysql - 如何连接多个外键?

转载 作者:行者123 更新时间:2023-11-29 06:37:39 24 4
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我正在使用 PHP 和 SQL 创建一个博客,我试图在 1 个 SQL 查询中查询所有内容,以便我可以显示作者的所有评论以及作者的所有博客。它们每个都有 user.uuid 作为外键。

我的博客表如下所示:

CREATE TABLE `blogs` (
`uuid` int(255) NOT NULL,
`title` varchar(1024) NOT NULL,
`detail` varchar(1024) NOT NULL,
`user_id` int(255) NOT NULL,
`created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

我的博客评论表如下所示:

CREATE TABLE `blogs_comments` (
`uuid` int(255) NOT NULL,
`blog_uuid` int(255) NOT NULL,
`user_uuid` int(255) NOT NULL,
`comment` varchar(250) NOT NULL,
`created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

我的用户表如下所示:

CREATE TABLE `users` (
`uuid` int(255) NOT NULL,
`username` varchar(15) COLLATE utf8_unicode_ci NOT NULL,
`password` varchar(64) COLLATE utf8_unicode_ci NOT NULL,
`foreName` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
`surName` varchar(30) COLLATE utf8_unicode_ci NOT NULL,
`email` text COLLATE utf8_unicode_ci NOT NULL,
`number` int(11) NOT NULL,
`created` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`is_admin` tinyint(1) NOT NULL DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;

这是我当前的 SQL:

SELECT
b.uuid AS 'Blog ID', b.title AS 'Blog Title', b.detail AS 'Blog Body', u.uuid AS 'Blog Author ID', u.username AS 'Blog Author Username',
(SELECT bc.comment WHERE u.uuid = bc.user_uuid) AS 'Comment',
(SELECT u.uuid WHERE u.uuid = bc.user_uuid) AS 'Comment Author ID',
(SELECT u.username WHERE u.uuid = bc.user_uuid) AS 'Comment Author Username'
FROM blogs b
INNER JOIN blogs_comments bc ON b.uuid = bc.blog_uuid
INNER JOIN users u ON b.user_id = u.uuid

查询工作正常,但是,它有一个意外的输出,如下所示:

我希望输出将评论作者的所有评论放在一行中,然后每一行将特定于评论作者。 IE:

Comment Author    Comment        Comment
Jaquarh TEST Lorem Ipsum

最佳答案

您需要知道每次会有多少评论,但如果您这样做,数据透视表可能会为您提供所需的内容。我对您的查询结构有点困惑,但我认为它可能看起来像这样带有枢轴:

SELECT
blog_id AS 'Blog ID',
title AS 'Blog Title',
detail AS 'Blog Body',
blog_author_id AS 'Blog Author ID',
username AS 'Blog Author Username',
Comment_Author_ID AS 'Comment Author ID',
Comment_Author_Username AS 'Comment Author Username',
[0] AS 'Comment 1',
[1] AS 'Comment 2',
[2] AS 'Comment 3',
[3] AS 'Comment 4',
[4] AS 'Comment 5',
[5] AS 'Comment 6'

FROM
(SELECT --A1
b.uuid as blog_id, b.title, b.detail, u.uuid as blog_author_id, u.username,
(SELECT bc.comment WHERE u.uuid = bc.user_uuid) AS Comment,
(SELECT u.uuid WHERE u.uuid = bc.user_uuid) AS Comment_Author_ID,
(SELECT u.username WHERE u.uuid = bc.user_uuid) AS Comment_Author_Username,
row_number() over(partition by b.uuid order by bc.comment) AS row_num
FROM blogs b
INNER JOIN blogs_comments bc ON b.uuid = bc.blog_uuid
INNER JOIN users u ON b.user_id = u.uuid AND u.uuid = bc.user_uuid
) as A1
PIVOT
(max([comment]) FOR row_num in ([0], [1], [2], [3], [4], [5])) AS pvt

这篇文章可能对您也有帮助:https://learn.microsoft.com/en-us/sql/t-sql/queries/from-using-pivot-and-unpivot?view=sql-server-2017

关于mysql - 如何连接多个外键?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/53109547/

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