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CREATE TABLE parent (
id INT PRIMARY KEY,
KEY (id)
) ENGINE=InnoDB;
CREATE TABLE child (
id INT PRIMARY KEY,
parent_id INT,
FOREIGN KEY (parent_id)
REFERENCES parent(id)
) ENGINE=InnoDB;
INSERT INTO parent VALUES (1);
INSERT INTO child VALUES (1,1);
SET SESSION foreign_key_checks = 0;
INSERT INTO child VALUES (2,2);
SELECT COUNT(*) = 1 FROM child WHERE id = 2;
COUNT(*) = 1
1
INSERT INTO child VALUES (3,3);
ERROR 23000: Cannot add or update a child row: a foreign key constraint fails (`test`.`child`, CONSTRAINT `child_ibfk_1` FOREIGN KEY (`parent_id`) REFERENCES `parent` (`id`))
SET SESSION foreign_key_checks = 0;
DELETE FROM parent;
SELECT COUNT(*) = 0 FROM parent;
COUNT(*) = 0
1
DROP TABLE child;
DROP TABLE parent;
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