SET @userstat.save= @@userstat;

set global userstat= 1;

create or replace table t (a int, key(a)) engine=MyISAM;

insert into t values (1),(2),(3),(4);

flush index_statistics;

select a from t where a in ( select a from t );

show index_statistics;

# Cleanup

drop table t;

set global userstat= @userstat.save;

MariaDB [test]> flush index_statistics;

Query OK, 0 rows affected (0.000 sec)

MariaDB [test]> select a from t where a in ( select a from t );

+------+

| a    |

+------+

|    1 |

|    2 |

|    3 |

|    4 |

+------+

4 rows in set (0.001 sec)

MariaDB [test]> show index_statistics;

+--------------+------------+------------+-----------+---------+

| Table_schema | Table_name | Index_name | Rows_read | Queries |

+--------------+------------+------------+-----------+---------+

| test         | t          | a          |         8 |       2 |

+--------------+------------+------------+-----------+---------+

1 row in set (0.001 sec)