I have run into more than one database that has both MyISAM and InnoDB tables and I’m very happy to know that I can change all of them into InnoDB–providing it’s at least MySQL 5.6.4.
This little, practical article from Kinsta tells how and has more detail, but basically, you can just change it from a dropdown once you’re in phpMyAdmin, or you can use:
ALTER TABLE wp_comments ENGINE=InnoDB;
wp_comments as an example.
This will help me streamline some old DBs! \o/
If you want to read more about databases and WordPress, Delicious Brains has a nice article about it, which is also where I got the link to the Kinsta one.