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CREATE TABLE parent (a INT PRIMARY KEY) ENGINE=InnoDB;
INSERT INTO parent SET a=1;
CREATE TABLE child (a INT PRIMARY KEY, FOREIGN KEY (a) REFERENCES parent(a)
ON UPDATE CASCADE)
ENGINE=InnoDB;
INSERT INTO child SET a=1;
TRUNCATE TABLE parent;
ERROR 42000: Cannot truncate a table referenced in a foreign key constraint (`test`.`child`, CONSTRAINT `child_ibfk_1` FOREIGN KEY (`a`) REFERENCES `test`.`parent` (`a`))
TRUNCATE TABLE child;
INSERT INTO child SET a=1;
UPDATE parent SET a=2;
SELECT * FROM child;
a
2
connect dml,localhost,root;
SET DEBUG_SYNC='foreign_constraint_update_cascade SIGNAL fk WAIT_FOR go';
UPDATE parent SET a=3;
connection default;
SET DEBUG_SYNC='now WAIT_FOR fk';
SET lock_wait_timeout=1;
TRUNCATE TABLE child;
ERROR HY000: Lock wait timeout exceeded; try restarting transaction
SET DEBUG_SYNC='now SIGNAL go';
connection dml;
SELECT * FROM child;
a
3
SET DEBUG_SYNC='foreign_constraint_check_for_update SIGNAL fk WAIT_FOR go';
DELETE FROM parent;
connection default;
SET DEBUG_SYNC='now WAIT_FOR fk';
TRUNCATE TABLE child;
ERROR HY000: Lock wait timeout exceeded; try restarting transaction
SET DEBUG_SYNC='now SIGNAL go';
connection dml;
ERROR 23000: Cannot delete or update a parent row: a foreign key constraint fails (`test`.`child`, CONSTRAINT `child_ibfk_1` FOREIGN KEY (`a`) REFERENCES `parent` (`a`) ON UPDATE CASCADE)
SELECT * FROM child;
a
3
INSERT INTO parent SET a=5;
SET DEBUG_SYNC='foreign_constraint_check_for_ins SIGNAL fk WAIT_FOR go';
INSERT INTO child SET a=5;
connection default;
SET DEBUG_SYNC='now WAIT_FOR fk';
SET foreign_key_checks=0;
TRUNCATE TABLE parent;
SET DEBUG_SYNC='now SIGNAL go';
connection dml;
ERROR 23000: Cannot add or update a child row: a foreign key constraint fails (`test`.`child`, CONSTRAINT `child_ibfk_1` FOREIGN KEY (`a`) REFERENCES `parent` (`a`) ON UPDATE CASCADE)
SELECT * FROM parent;
a
SELECT * FROM child;
a
3
disconnect dml;
connection default;
SET DEBUG_SYNC = RESET;
DROP TABLE child, parent;
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