I will be updating this gist as I dig deeper into the optimization planner. My research will be strictily bound to SELECT qeury right now.
When running an explain query, you can find the output like ->
MariaDB [sample_db]> explain select * from sample_table;
+------+-------------+--------------+------+---------------+------+---------+------+------+-------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+--------------+------+---------------+------+---------+------+------+-------+