mysql forige key

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[Òý]MySQL INNODBÀàÐͱíµÄÍâ¼ü¹ØÁªÉèÖÃ

Here is a simple example that relates parent and child tables through a single-column foreign key:
CREATE TABLE parent (id INT NOT NULL,
                     PRIMARY KEY (id)
) ENGINE=INNODB;
CREATE TABLE child (id INT, parent_id INT,
                    INDEX par_ind (parent_id),
                    FOREIGN KEY (parent_id) REFERENCES parent(id)
                      ON DELETE CASCADE
) ENGINE=INNODB;
A more complex example in which a product_order table has foreign keys for two other tables.
One foreign key references a two-column index in the product table.
The other references a single-column index in the customer table:
CREATE TABLE product (category INT NOT NULL, id INT NOT NULL,
                      price DECIMAL,
                      PRIMARY KEY(category, id)) ENGINE=INNODB;
CREATE TABLE customer (id INT NOT NULL,
                       PRIMARY KEY (id)) ENGINE=INNODB;
CREATE TABLE product_order (no INT NOT NULL AUTO_INCREMENT,
                            product_category INT NOT NULL,