CREATE TABLE t1(f1 INT NOT NULL, f2 INT NOT NULL,
PRIMARY KEY(f1))ENGINE=InnoDB;
INSERT INTO t1 VALUES(1, 2), (2, 2);
SET DEBUG_SYNC="innodb_rollback_inplace_alter_table SIGNAL dml_start WAIT_FOR dml_commit";
ALTER TABLE t1 ADD UNIQUE KEY(f2);
connect con1,localhost,root,,,;
SET DEBUG_SYNC="now WAIT_FOR dml_start";
BEGIN;
DELETE FROM t1;
SET DEBUG_SYNC="now SIGNAL dml_commit";
connection default;
ERROR 23000: Duplicate entry '2' for key 'f2'
connection con1;
COMMIT;
TRUNCATE TABLE t1;
SET unique_checks=0, foreign_key_checks=0;
BEGIN;
INSERT INTO t1 VALUES(1, 2);
ROLLBACK;
connection default;
SELECT * FROM t1;
f1	f2
SHOW CREATE TABLE t1;
Table	Create Table
t1	CREATE TABLE `t1` (
  `f1` int(11) NOT NULL,
  `f2` int(11) NOT NULL,
  PRIMARY KEY (`f1`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
disconnect con1;
DROP TABLE t1;
SET DEBUG_SYNC=RESET;