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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;
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