set global userstat=1;
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;
insert into just_a_test values(1,'fa','la','china_a',11111111,'fa_la@163.com'),
(2,'fb','lb','china_b',22222222,'fb_lb@163.com'),
(3,'fc','lc','china_c',33333333,'fc_lc@163.com'),
(4,'fd','ld','china_d',44444444,'fd_ld@163.com'),
(5,'fe','le','china_e',55555555,'fe_le@163.com');
alter table just_a_test add primary key (id);
alter table just_a_test add key IND_just_a_test_first_name_last_name(first_name,last_name);

select * from information_schema.index_statistics;
# Empty set (0.00 sec)

select count(*) from just_a_test where first_name='fc' and last_name='lc';
# +----------+
# | count(*) |
# +----------+
# |        1 |
# +----------+
# 1 row in set (0.03 sec)

select * from information_schema.index_statistics;
# +--------------+-------------+--------------------------------------+-----------+
# | TABLE_SCHEMA | TABLE_NAME  | INDEX_NAME                           | ROWS_READ |
# +--------------+-------------+--------------------------------------+-----------+
# | test         | just_a_test | IND_just_a_test_first_name_last_name |         1 |
# +--------------+-------------+--------------------------------------+-----------+

alter table just_a_test drop key IND_just_a_test_first_name_last_name;

select * from information_schema.index_statistics where table_schema='test' and table_name='just_a_test';
# +--------------+-------------+--------------------------------------+-----------+
# | TABLE_SCHEMA | TABLE_NAME  | INDEX_NAME                           | ROWS_READ |
# +--------------+-------------+--------------------------------------+-----------+
# | test         | just_a_test | IND_just_a_test_first_name_last_name |         1 |
# +--------------+-------------+--------------------------------------+-----------+
# 1 row in set (0.00 sec)

drop table test.just_a_test;

select * from information_schema.index_statistics where table_schema='test' and table_name='just_a_test';
# +--------------+-------------+--------------------------------------+-----------+
# | TABLE_SCHEMA | TABLE_NAME  | INDEX_NAME                           | ROWS_READ |
# +--------------+-------------+--------------------------------------+-----------+
# | test         | just_a_test | IND_just_a_test_first_name_last_name |         1 |
# +--------------+-------------+--------------------------------------+-----------+
# 1 row in set (0.00 sec)