So you have the need for a SQL database for your website (or whatever), which all happens to be a Zentyal box. Why not just use the existing mySQL server? Why not indeed? All you need is the password. Luck would have it that is not a problem.
sudo nano /var/lib/zentyal/conf/zentyal-mysql.passwd
Copy that down cause thats your password. From here you can use the database manually or install something like phpMyadmin.
I found this page to be of help when I was searching: