CREATE TABLE t(id INT NOT NULL, col1 INT, col2 INT NOT NULL, PRIMARY KEY(id, col2), UNIQUE KEY uk(col2)) ENGINE=XENGINE;
INSERT INTO t VALUES(1, 2, 2), (2, 4, 4);
SELECT * FROM t;
id	col1	col2
1	2	2
2	4	4
EXPLAIN SELECT col2 FROM t;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t	NULL	index	NULL	uk	4	NULL	#	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t`.`col2` AS `col2` from `test`.`t`
SELECT col2 FROM t;
col2
2
4
SET DEBUG_SYNC= 'xengine.inplace_populate_indexes_done SIGNAL start_dml WAIT_FOR dml_done';
ALTER TABLE t DROP COLUMN col1;
# Switch to dml connection
SET DEBUG_SYNC= 'now WAIT_FOR start_dml';
UPDATE t SET col2=6 WHERE col2=4;
SELECT * FROM t;
id	col1	col2
1	2	2
2	4	6
EXPLAIN SELECT col2 FROM t;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t	NULL	index	NULL	uk	4	NULL	#	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t`.`col2` AS `col2` from `test`.`t`
SELECT col2 FROM t;
col2
2
6
SET DEBUG_SYNC= 'now SIGNAL dml_done';
CHECK TABLE t;
Table	Op	Msg_type	Msg_text
test.t	check	status	OK
SHOW CREATE TABLE t;
Table	Create Table
t	CREATE TABLE `t` (
  `id` int(11) NOT NULL,
  `col2` int(11) NOT NULL,
  PRIMARY KEY (`id`,`col2`),
  UNIQUE KEY `uk` (`col2`)
) ENGINE=XENGINE DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci
SELECT * FROM t;
id	col2
1	2
2	6
EXPLAIN SELECT col2 FROM t;
id	select_type	table	partitions	type	possible_keys	key	key_len	ref	rows	filtered	Extra
1	SIMPLE	t	NULL	index	NULL	uk	4	NULL	#	100.00	Using index
Warnings:
Note	1003	/* select#1 */ select `test`.`t`.`col2` AS `col2` from `test`.`t`
SELECT col2 FROM t;
col2
2
6
DROP TABLE t;