1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
|
CREATE TABLE t1 (D INT) ENGINE=innodb;
INSERT INTO t1 VALUES (10);
ALTER TABLE t1 MODIFY COLUMN d INT;
ALTER TABLE t1 ADD INDEX my_d (d);
SHOW CREATE TABLE t1;
Table Create Table
t1 CREATE TABLE `t1` (
`d` int(11) DEFAULT NULL,
KEY `my_d` (`d`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci
INSERT INTO t1 VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9);
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
EXPLAIN SELECT d FROM t1 WHERE d = 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref my_d my_d 5 const 128 Using index
EXPLAIN SELECT D FROM t1 WHERE D = 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref my_d my_d 5 const 128 Using index
ALTER TABLE t1 DROP INDEX my_d;
ALTER TABLE t1 MODIFY COLUMN D INT;
ANALYZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
ALTER TABLE t1 ADD INDEX my_d (D);
EXPLAIN SELECT d FROM t1 WHERE d = 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref my_d my_d 5 const 128 Using index
EXPLAIN SELECT D FROM t1 WHERE D = 5;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref my_d my_d 5 const 128 Using index
SHOW CREATE TABLE t1;
Table Create Table
t1 CREATE TABLE `t1` (
`D` int(11) DEFAULT NULL,
KEY `my_d` (`D`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_uca1400_ai_ci
DROP TABLE t1;
|
