Hint NO_INDEX() disables all indexes if none of given index names is resolved

CREATE TABLE t1 (

  a INT,

  b INT,

  PRIMARY KEY(a),

  KEY ab(a, b)

);

INSERT INTO t1 VALUES (1,1),(2,2),(3,3),(4,4);

INSERT INTO t1 SELECT a + 4, b + 4 FROM t1;

INSERT INTO t1 SELECT a + 8, b + 8 FROM t1;

INSERT INTO t1 SELECT a +16, b +16 FROM t1;

INSERT INTO t1 SELECT a +32, b +32 FROM t1;

INSERT INTO t1 SELECT a +64, b +64 FROM t1;

analyze table t1;

EXPLAIN EXTENDED SELECT a FROM t1 GROUP BY a;

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1 PRIMARY) */ a FROM t1 GROUP BY a;

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1) */ a FROM t1 GROUP BY a;

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1 a) */ a FROM t1 GROUP BY a;

drop table t1;

EXPLAIN EXTENDED SELECT a FROM t1 GROUP BY a;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	index	NULL	PRIMARY	4	NULL	128	100.00	Using index

Warnings:

Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` group by `test`.`t1`.`a`

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1 PRIMARY) */ a FROM t1 GROUP BY a;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	index	NULL	ab	9	NULL	128	100.00	Using index

Warnings:

Note	1003	select /*+ NO_INDEX(`t1`@`select#1` `PRIMARY`) */ `test`.`t1`.`a` AS `a` from `test`.`t1` group by `test`.`t1`.`a`

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1) */ a FROM t1 GROUP BY a;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	128	100.00	Using filesort

Warnings:

Note	1003	select /*+ NO_INDEX(`t1`@`select#1`) */ `test`.`t1`.`a` AS `a` from `test`.`t1` group by `test`.`t1`.`a`

EXPLAIN EXTENDED SELECT/*+ NO_INDEX(t1 a) */ a FROM t1 GROUP BY a;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	128	100.00	Using filesort

Warnings:

Warning	4222	Unresolved index name `t1`@`select#1` `a` for NO_INDEX hint

Note	1003	select /*+ NO_INDEX(`t1`@`select#1` `a`) */ `test`.`t1`.`a` AS `a` from `test`.`t1` group by `test`.`t1`.`a`