create table in mysql with foreign key code example

Example 1: alter table add foreign key mysql

ALTER TABLE orders
ADD 
FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE;

Example 2: mysql change foreign key

ALTER TABLE Orders
ADD FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

Example 3: add constraint fk

ALTER TABLE Orders
ADD CONSTRAINT FK_PersonOrder
FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

Example 4: how to connect database foreign key in mysql

CREATE TABLE products(
    productId INT AUTO_INCREMENT PRIMARY KEY,
    productName varchar(100) not null,
    categoryId INT NOT NULL,
    CONSTRAINT fk_category
    FOREIGN KEY (categoryId) 
    REFERENCES categories(categoryId)
        ON UPDATE CASCADE
        ON DELETE CASCADE
) ENGINE=INNODB;

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