The default "localhost" should work here, but there are several reasons why it doesn't. The same reasons would apply to specifying the hostname given by "hostname".
First, make sure mysql is installed: "which mysql". If it isn't, install it from GSlapt.
Then there's a lot more reading to do. Here's a place to start:http://www.mythtv.org/wiki/MythTV-HOWTO#Setting_up_the_initial_database
There's much more to do. I think much of it should have been done during MythTV package installation, but in this case it's hard to know for sure.
Each time you find more of the answer, you might want to do rm -r ~/.mythtv
(as your regular user, not root). It will be recreated with defaults each time you run MythTV setup.
Wish I had better news.