How to store the data of mysql on OS X in an encrypted state?

If you'd like it to be used in the same manner as FileVault (unencrypted on login, encrypted automatically on logout), just move the data to somewhere in your user homedirectory, get your permissions set up right, and then symlink to the data from the default location.

If you just want to make an encrypted archive, you could do that with an encrypted DMG from Disk Utility.

If you just want fields encrypted you could do something like this: https://web.archive.org/web/1/http://articles.techrepublic%2ecom%2ecom/5100-10878_11-6124013.html

The article describes using the encode or encrypt method for field contents.

Truecrypt would let you move it into a encrypted virtual partition...