How to not start a service by default

Use case: in my laptop, I sometimes need MySQL, PostgreSQL or Apache in order to test some software that I'm developing, but I do not want them on all the time.

The solution is: rm /etc/rc*.d/S*mysql* (thanks to Wouter)

update-rc.d will not touch your symlinks as long as there is at least one still around for a package. Also, this leaves the stop symlinks around, so that when I start one of these services for development, it will still be properly stopped on shutdown.