我有 3 个 MySQL 表,我想将它们连接在一起。
类(class):
CREATE TABLE `library_classes` (
`id` int NOT NULL AUTO_INCREMENT,
`name` varchar(255) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;
INSERT INTO `library_classes` (`id`, `name`) VALUES
(1, 'Tolkien'),
(2, 'CS Lewis');
session :
CREATE TABLE `library_sessions` (
`id` int NOT NULL AUTO_INCREMENT,
`class_id` int NOT NULL,
`session_timestamp` timestamp NOT NULL,
PRIMARY KEY (`id`),
KEY `class_id` (`class_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;
INSERT INTO `library_sessions` (`id`, `class_id`, `session_timestamp`) VALUES
(1, 1, '2023-08-01 15:30:00'),
(2, 2, '2023-08-02 10:15:00'),
(3, 1, '2023-08-04 09:30:00');
预订:
CREATE TABLE `library_bookings` (
`id` int NOT NULL AUTO_INCREMENT,
`session_id` int NOT NULL,
`email` varchar(255) NOT NULL,
`datetime_submitted` timestamp NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3;
INSERT INTO `library_bookings` (`id`, `session_id`, `email`) VALUES
(1, 1, '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="513b3e223411363c30383d7f323e3c" rel="noreferrer noopener nofollow">[email protected]</a>'),
(2, 2, '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="d4beb5bab194adb5bcbbbbfab7bbb9" rel="noreferrer noopener nofollow">[email protected]</a>'),
(3, 2, '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="771d181f19371f18031a161e1b5914181a" rel="noreferrer noopener nofollow">[email protected]</a>');
何时 <a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="660c09150326010b070f0a4805090b" rel="noreferrer noopener nofollow">[email protected]</a>
已登录,我希望我的页面如下所示:
Tolkien | 2023-08-01 15:30:00 | CANCEL
CS Lewis | 2023-08-02 10:15:00 | BOOK NOW
Tolkien | 2023-08-04 09:30:00 | BOOK NOW
最佳答案
我已将您的数据导入到 SQLFIDDLE ;
以下查询将为您提供预期的结果。
select lc.name, ls.session_timestamp,
if(lb.id is null, 'BOOK NOW', 'CANCEL') as booking_status
from library_classes lc
join library_sessions ls on lc.id = ls.class_id
left join library_bookings lb on ls.id = lb.session_id and lb.email = '<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="117b7e627451767c70787d3f727e7c" rel="noreferrer noopener nofollow">[email protected]</a>'
order by ls.session_timestamp;
它给出的预期输出为:
name session_timestamp booking_status
Tolkien 2023-08-01T15:30:00Z CANCEL
CS Lewis 2023-08-02T10:15:00Z BOOK NOW
Tolkien 2023-08-04T09:30:00Z BOOK NOW
关于mysql - SQL - 基本内连接查询,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/75684833/