CREATE TABLE t1(
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
a CHAR(1) NOT NULL,
b CHAR(36) NOT NULL) ENGINE=InnoDB;
INSERT INTO t1(a,b) VALUES ('a','b');
INSERT INTO t1(a,b) SELECT a,b FROM t1;
INSERT INTO t1(a,b) SELECT a,b FROM t1;
INSERT INTO t1(a,b) SELECT a,b FROM t1;
INSERT INTO t1(a,b) SELECT a,b FROM t1;
ALTER TABLE t1 ADD KEY (a);
affected rows: 0
info: Records: 0  Duplicates: 0  Warnings: 0
EXPLAIN SELECT COUNT(*) FROM t1, t1 t2 WHERE t1.a = t2.a AND t1.b = t2.b;
id	1
select_type	SIMPLE
table	t1
type	ALL
possible_keys	a
key	NULL
key_len	NULL
ref	NULL
rows	16
Extra	
id	1
select_type	SIMPLE
table	t2
type	ref
possible_keys	a
key	a
key_len	1
ref	test.t1.a
rows	1
Extra	Using where
ALTER TABLE t1 DROP KEY a;
SET expand_fast_index_creation = 1;
SELECT @@expand_fast_index_creation;
@@expand_fast_index_creation
1
ALTER TABLE t1 ADD KEY (a);
affected rows: 0
info: Records: 0  Duplicates: 0  Warnings: 0
EXPLAIN SELECT COUNT(*) FROM t1, t1 t2 WHERE t1.a = t2.a AND t1.b = t2.b;
id	1
select_type	SIMPLE
table	t1
type	ALL
possible_keys	a
key	NULL
key_len	NULL
ref	NULL
rows	16
Extra	
id	1
select_type	SIMPLE
table	t2
type	ALL
possible_keys	a
key	NULL
key_len	NULL
ref	NULL
rows	16
Extra	Using where; Using join buffer
SET expand_fast_index_creation = 0;
DROP TABLE t1;