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set global userstat=1;
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create table just_a_test(id int,first_name varchar(10),last_name varchar(10),address varchar(100),phone bigint,email varchar(30)) engine =innodb;
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insert into just_a_test values(1,'fa','la','china_a',11111111,'fa_la@163.com'),
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(2,'fb','lb','china_b',22222222,'fb_lb@163.com'),
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(3,'fc','lc','china_c',33333333,'fc_lc@163.com'),
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(4,'fd','ld','china_d',44444444,'fd_ld@163.com'),
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(5,'fe','le','china_e',55555555,'fe_le@163.com');
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alter table just_a_test add primary key (id);
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alter table just_a_test add key IND_just_a_test_first_name_last_name(first_name,last_name);
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select * from information_schema.index_statistics;
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# Empty set (0.00 sec)
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select count(*) from just_a_test where first_name='fc' and last_name='lc';
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# +----------+
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# | count(*) |
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# +----------+
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# | 1 |
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# +----------+
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# 1 row in set (0.03 sec)
|
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select * from information_schema.index_statistics;
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# +--------------+-------------+--------------------------------------+-----------+
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# | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |
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# +--------------+-------------+--------------------------------------+-----------+
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# | test | just_a_test | IND_just_a_test_first_name_last_name | 1 |
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# +--------------+-------------+--------------------------------------+-----------+
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Step X
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alter table just_a_test drop key IND_just_a_test_first_name_last_name;
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select * from information_schema.index_statistics where table_schema='test' and table_name='just_a_test';
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# +--------------+-------------+--------------------------------------+-----------+
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# | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |
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# +--------------+-------------+--------------------------------------+-----------+
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# | test | just_a_test | IND_just_a_test_first_name_last_name | 1 |
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# +--------------+-------------+--------------------------------------+-----------+
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# 1 row in set (0.00 sec)
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Step Y
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drop table test.just_a_test;
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select * from information_schema.index_statistics where table_schema='test' and table_name='just_a_test';
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# +--------------+-------------+--------------------------------------+-----------+
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# | TABLE_SCHEMA | TABLE_NAME | INDEX_NAME | ROWS_READ |
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# +--------------+-------------+--------------------------------------+-----------+
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# | test | just_a_test | IND_just_a_test_first_name_last_name | 1 |
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# +--------------+-------------+--------------------------------------+-----------+
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# 1 row in set (0.00 sec)
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Why could step X show informations about index that couldn't existed?
Why could step Y show informations about table that couldn't existed?
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