mysql startup issue

I was to startup mysql today via System Preference GUI. However, After I click the "Start the MySQL Server" button, it stuck for a while but didn't show the success message as usual. I am perplexed by it because I did not do anything I could come up with
that may impact the DB. I used the cmd to start the MySQL:

sudo mysqld start --user root

There are error messages indicating the port is already in use. I tried to find out which process/program was listening 3306 port by

sudo lsof -n -i4TCP:3306 | grep LISTEN

It says Zend is listening port 3306. I recalled that I installed Zend Server yesterday but I could not associate that with the DB issue until I removed the Zend Server from Application and uninstalled it by

sudo /usr/local/zend/bin/uninstall.sh

Then I restart the DB and this time it works! It seems the Zend Server has its own mysql running after OS startup.