A MySQL database creates a number of different data files in the mysql data directory (typically /var/lib/mysql). The following are the differences between the data files created:
| File Extension | Purpose |
|---|---|
| .frm | table definition |
| .MYD | table data |
| .MYI | table indices |
I believe these files are created for both MyISAM and InnoDB table types because the MySQL documentation references these types with respect to MyISAM and I definitely see them on my InnoDB tables.
I couldn’t find this information directly in the MySQL documentation and google wasn’t much help either so hopefully this post will save someone else some search effort.