如何使 2 个或更多相同类型的列具有唯一的值组合 MySQL答案

【问题标题】：How can I make 2 or more columns of the same type have have unique value combinations MySQL如何使 2 个或更多相同类型的列具有唯一的值组合 MySQL
【发布时间】：2022-10-07 14:38:08
【问题描述】：

我有这两张桌子：

CREATE TABLE `locations`(
    `location_id` INT NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`location_id`)
);

CREATE TABLE IF NOT EXISTS `routes`(
    `route_id` INT NOT NULL AUTO_INCREMENT,
    `location_id_1` INT NOT NULL,
    `location_id_2` INT NOT NULL,
    FOREIGN KEY (`location_id_1`) 
        REFERENCES `locations` (`location_id`)
        ON UPDATE CASCADE
        ON DELETE CASCADE,
    FOREIGN KEY (`location_id_2`) 
        REFERENCES `locations` (`location_id`)
        ON UPDATE CASCADE
        ON DELETE CASCADE,
    UNIQUE KEY(`location_id_1`, `location_id_2`),
    PRIMARY KEY (`route_id`)
);

我想在routes 表上是否有以下记录：

+---------------+---------------+
| location_id_1 | location_id_2 |
+---------------+---------------+
|             1 |             2 |
+---------------+---------------+

那么下面的记录不应该被允许：

+---------------+---------------+
| location_id_1 | location_id_2 |
+---------------+---------------+
|             2 |             1 |
+---------------+---------------+

请让我知道如何解决这个问题，即使这意味着我必须重组我的表格

是什么导致不允许第二条记录？任一列中是否存在 1 或 2？或两者？ (1,2) 与 (2,1) 不同，因此如果有额外的上下文可能会有所帮助，尤其是在 uhm 表上进行架构重组的情况下。 :)
如果已经在任一列上设置了 1 和 2 的组合，则不应在后面的记录中允许它。
解决方案 1 - 功能唯一索引。解决方案 2 - 如果 value1 > value2，则交换值的唯一索引和触发器。解决方案 3 - 唯一索引 + CHECK 约束。还有更多解决方案...

标签： mysql sql database

【解决方案1】：

CREATE TABLE `locations`(
    `location_id` INT NOT NULL AUTO_INCREMENT,
    PRIMARY KEY (`location_id`)
);

CREATE TABLE IF NOT EXISTS `routes`(
    `route_id` INT NOT NULL AUTO_INCREMENT,
    `location_id_1` INT NOT NULL,
    `location_id_2` INT NOT NULL,
    FOREIGN KEY (`location_id_1`) 
        REFERENCES `locations` (`location_id`)
        ON UPDATE CASCADE
        ON DELETE CASCADE,
    FOREIGN KEY (`location_id_2`) 
        REFERENCES `locations` (`location_id`)
        ON UPDATE CASCADE
        ON DELETE CASCADE,
    UNIQUE KEY( (LEAST(`location_id_1`, `location_id_2`)),
                (GREATEST(`location_id_1`, `location_id_2`))),
    PRIMARY KEY (`route_id`)
);

INSERT INTO locations VALUES (1), (2);
INSERT INTO routes VALUES (1,1,2);

INSERT INTO routes VALUES (2,2,1);

Duplicate entry '1-2' for key 'routes.functional_index'

fiddle

【讨论】：