connection node_2;
connection node_1;
CREATE TABLE parent (
id INT NOT NULL,
PRIMARY KEY (id)
) ENGINE=InnoDB;
CREATE TABLE child (
id INT, 
parent_id INT,
FOREIGN KEY (parent_id) 
REFERENCES parent(id)
ON UPDATE SET NULL
ON DELETE SET NULL
) ENGINE=InnoDB;
INSERT INTO parent VALUES (1),(2);
INSERT INTO child VALUES (1,1),(2,2);
connection node_2;
DELETE FROM parent WHERE id = 1;
SELECT parent_id IS NULL FROM child WHERE id = 1;
parent_id IS NULL
1
connection node_1;
SELECT parent_id IS NULL FROM child WHERE id = 1;
parent_id IS NULL
1
UPDATE parent SET id = 3 WHERE id = 2;
SELECT parent_id IS NULL FROM child WHERE id = 2;
parent_id IS NULL
1
connection node_2;
SELECT parent_id IS NULL FROM child WHERE id = 2;
parent_id IS NULL
1
connection node_1;
DROP TABLE child;
DROP TABLE parent;