[ Avaa Bypassed ]

CREATE TABLE parent (a INT PRIMARY KEY, b INT NOT NULL) ENGINE = InnoDB;
INSERT INTO parent VALUES(1,2),(2,2);
CREATE TABLE child (a INT PRIMARY KEY, b INT NOT NULL) ENGINE = InnoDB;
INSERT INTO child VALUES (10, 2);
SET DEBUG_SYNC = 'innodb_inplace_alter_table_enter SIGNAL start_create
WAIT_FOR go_ahead';
CREATE UNIQUE INDEX idx ON parent(b);;
SET DEBUG_SYNC = 'now WAIT_FOR start_create';
INSERT INTO parent VALUES(4, 2);
SET DEBUG_SYNC = 'now SIGNAL go_ahead';
ERROR 23000: Duplicate entry '2' for key 'idx'
SET DEBUG_SYNC = 'now SIGNAL conn_add_fk';
SET DEBUG_SYNC = 'now WAIT_FOR conn_add_fk';
ALTER TABLE child ADD CONSTRAINT cfx FOREIGN KEY (b) REFERENCES parent(b);
ERROR HY000: Cannot add foreign key constraint
DROP TABLE child;
DROP TABLE parent;