adding foreign key constraint mysql code example

Example 1: foreign key mySql

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;

Example 2: update foreign key value in mysql

SET foreign_key_checks = 0;
UPDATE languages SET id='xyz' WHERE id='abc';
UPDATE categories_languages SET language_id='xyz' WHERE language_id='abc';
SET foreign_key_checks = 1;