具有外键在 table 1 中的约束不是 table 2 中的外键

Question

我有一个 table 属性，现在有两个 table 的 Rent 和 sale，每个都有 property_id 作为外键。我如何保证 Rent 中的任何 property_id 都不能在 sale 中重复？如果是 MySQL 应该抛出错误。

这是租金Table，完全相似是销售

CREATE TABLE Rent
(
  /*some data*/
  Property_id INT NOT NULL,
  PRIMARY KEY (Property_id),
  FOREIGN KEY (Property_id) REFERENCES Property(Property_id) ON DELETE CASCADE
);

Answer 1

您可以将单个 table 与鉴别器列一起使用

示例

CREATE TABLE property (
    id   INT AUTO_INCREMENT,
    name VARCHAR(255),
    /* some data */
    PRIMARY KEY (id)
);

CREATE TABLE contract (
    id          INT AUTO_INCREMENT,
    property_id INT NOT NULL,
    type        VARCHAR(32) CHECK ( type IN ('rent', 'sale') ),
    PRIMARY KEY (id),
    FOREIGN KEY (property_id)
        REFERENCES property(id) ON DELETE CASCADE
);

CREATE TABLE Rent (
    id            INT AUTO_INCREMENT,
    /* some data */
    contract_id   INT NOT NULL,
    contract_type VARCHAR(32) CHECK ( contract_type = 'rent'),
    PRIMARY KEY (id),
    FOREIGN KEY (contract_id)
        REFERENCES contact(id) ON DELETE CASCADE
);

CREATE TABLE Sale (
    id            INT AUTO_INCREMENT,
    /* some data */
    contract_id   INT NOT NULL,
    contract_type VARCHAR(32) CHECK ( contract_type = 'sale'),
    PRIMARY KEY (id),
    FOREIGN KEY (contract_id)
        REFERENCES contact(id) ON DELETE CASCADE
);

具有外键在 table 1 中的约束不是 table 2 中的外键

Have constraints such that foreign key is in table 1 is not foreign key in table 2

mysql

sql

database-design

foreign-keys