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1CREATE TABLE IF NOT EXISTS `books` (
2`id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
3`name` TEXT NOT NULL,
4PRIMARY KEY (`id`)
5) ENGINE=InnoDB DEFAULT CHARSET=utf8;
6	
7CREATE TABLE IF NOT EXISTS `compare` (
8`id_1` BIGINT UNSIGNED NOT NULL,
9`id_2` BIGINT UNSIGNED NOT NULL, 
10PRIMARY KEY (`id_1`,`id_2`),
11FOREIGN KEY (`id_1`) REFERENCES books(`id`),
12FOREIGN KEY (`id_2`) REFERENCES books(`id`)
13) ENGINE=InnoDB DEFAULT CHARSET=utf8;
14	
15id_1 | id_2
16------------
17 1  |  2
18	
19id_1 | id_2
20------------
21 2  |  1