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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);
DELETE FROM parent WHERE id = 1;
SELECT parent_id IS NULL FROM child WHERE id = 1;
parent_id IS NULL
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
SELECT parent_id IS NULL FROM child WHERE id = 2;
parent_id IS NULL
1
DROP TABLE child;
DROP TABLE parent;
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