table

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;

INSERT INTO parent (id) VALUES (1);
INSERT INTO child (id, parent_id) VALUES (1,1);

DELETE FROM parent WHERE id = 1;

CREATE TABLE parent (
    id INT NOT NULL,
    name varchar(250) not null,
    parent_id INT NULL,
    FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE,
    PRIMARY KEY (id)
) ENGINE=INNODB

INSERT INTO parent (id,name,parent_id)
VALUES ('1', 'Test 1', NULL), ('2', 'Test 2', '1')

DELETE FROM parent WHERE id = 1;

DELIMITER //

CREATE TRIGGER delete_clean BEFORE DELETE ON Parent
FOR EACH ROW
BEGIN
  DELETE * FROM Parent WHERE Parent.parent_id = OLD.id;
END //

DELIMITER ;