So you're looking to install MySQL on your Ubuntu machine because you know how much MySQL rocks or because you want to link it up with Liferay or both. (Or neither. I dunno.)
There's a plethora of advice on the web on how to do this. "Easy!" They tell you "All you have to do is use the command
sudo apt-get install mysql-server
and you're good to go!"
So you happily get on your terminal, type in that command, enter your root password and all that and...
E: Can't find package mysql-server
So you restart your machine because one guy was able to get the packages to appear in the Synaptic Package Manager after doing that and that doesn't help. So you search for it in Synaptic and that doesn't help either. The fate of the world rests in you getting MySQL installed and suddenly that wonderful apt-get feature ain't looking too hot.
Well don't start the manual installation just yet, friends.
See, the problem is that MySQL is (as of the time I write this) on version 5.1 and that's included in the package name. No, you might not see it in Synaptic either. Use this command:
sudo apt-get install mysql-server-5.1
And watch the magic happen.