假设我有以下三个表:
CREATE TABLE user (
id INTEGER NOT NULL AUTO_INCREMENT,
/* ... */
PRIMARY KEY(id)
)
CREATE TABLE Account (
id INTEGER NOT NULL AUTO_INCREMENT,
user_id INTEGER NOT NULL,
/* ... */
PRIMARY KEY(id),
FOREIGN KEY(user_id) REFERENCES User(id)
)
CREATE TABLE Transfer (
id INTEGER NOT NULL AUTO_INCREMENT,
from_account INTEGER NOT NULL,
to_account INTEGER NOT NULL,
PRIMARY KEY(id),
FOREIGN KEY(from_account) REFERENCES Account(id),
FOREIGN KEY(to_account) REFERENCES Account(id),
CONSTRAINT ???
/* SELECT id FROM Account WHERE id=from_account == SELECT id FROM Account WHERE id=to_account */
)
顾名思义,转账应该引用两个帐户,但我想确保这两个帐户属于同一个人。创建表时如何解决这个问题?这可能吗?
最佳答案
不幸的是,您需要在传输表中重复user_id
:
CREATE TABLE Account (
id INTEGER NOT NULL AUTO_INCREMENT,
user_id INTEGER NOT NULL,
/* ... */
PRIMARY KEY (id),
FOREIGN KEY (user_id) REFERENCES User (id),
UNIQUE (user_id, id) -- redundant but needed for the foreign key constraint
);
CREATE TABLE Transfer (
id INTEGER NOT NULL AUTO_INCREMENT PRIMARY KEY,
user_id INTEGER,
from_account INTEGER NOT NULL,
to_account INTEGER NOT NULL,
FOREIGN KEY (user_id) REFERENCES User (id),
FOREIGN KEY (user_id, from_account) REFERENCES Account (user_id, id),
FOREIGN KEY (user_id, to_account) REFERENCES Account (user_id, id)
);
关于mysql - SQL约束: check if a bi-referenced table has common value,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/58821211/