如何创建也是MySQL主键的外键? [英] How to create foreign key that is also a primary key in MySQL?
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问题描述
pre $ code CREATE TABLE销售(
sale_id CHAR(40),
PRIMARY KEY(
折扣DOUBLE,
类型VARCHAR(255),
价格DOUBLE,
);
CREATE TABLE Normal_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id);
);
CREATE TABLE Special_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id);
);
我在这里错过了什么?
(
sale_id CHAR(40),
CREATE TABLE PRIMARY KEY(sale_id),
discount DOUBLE,
type VARCHAR(255),
price DOUBLE
)ENGINE = INNODB;
CREATE TABLE Normal_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
FOREIGN KEY(sale_id)参考销售(sale_id)
)ENGINE = INNODB;
CREATE TABLE Special_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
FOREIGN KEY(sale_id)参考销售(sale_id)
)ENGINE = INNODB;
只要确定你的数据库是 InnoDB
哪个支持外部参考。
This should be a fairly straightforward question, but I'm unable to find an easy answer. How do you create a foreign key that is also a primary key in MySQL? Here's my current attempt:
CREATE TABLE Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
discount DOUBLE,
type VARCHAR(255),
price DOUBLE,
);
CREATE TABLE Normal_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id);
);
CREATE TABLE Special_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id);
);
What am I missing here?
Thanks in advance.
解决方案
Add FOREIGN KEY (sale_id) REFERENCES Sale(sale_id)
to each foreign table:
CREATE TABLE Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
discount DOUBLE,
type VARCHAR(255),
price DOUBLE
) ENGINE=INNODB;
CREATE TABLE Normal_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
FOREIGN KEY (sale_id) REFERENCES Sale(sale_id)
) ENGINE=INNODB;
CREATE TABLE Special_Sale(
sale_id CHAR(40),
PRIMARY KEY(sale_id),
FOREIGN KEY (sale_id) REFERENCES Sale(sale_id)
) ENGINE=INNODB;
Just make sure your database is InnoDB
which supports Foreign References.
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