[Ubuntu] How to fix dependency problems

This is not a very generic method to solve dependency hells but in many obvious cases this is a very good one. It solved one of my problems with some components of "MySQL" being replaced / removed by some mysterious force. I'll pick the scenario here and try to draw a picture on the approach. The solution is based on the askUbuntu answer here [ http://askubuntu.com/questions/227978/problem-after-mysql-server-installation-i-cant-install-any-thing-in-ubuntu-12-04/228450#228450 ]

The problem: I was trying to access a web app that I was working on inside my 'localhost', but for some reason the mysql components were not functioning properly.
The server configuration: Apache2, PHP5, MySQL. The server was setup using 'Automatic virtual hosting' method.
The packages used were installed using:

apt-get install ia32-libs-multiarch build-essential ncurses-term g++ mc lfm unrar firefox apache2 apache2-doc apache2-suexec git zsh vim aria2 awesome curl chromium-browser mpd ncmpcpp git conky pcregrep unagi mysql-server libapache2-mod-auth-mysql php5-mysql php5 php-pear php5-sqlite php5-curl php5-imap php5-intl php5-mysql phpmyadmin openssh-server php5-mcrypt 

It's the full string from my server setup script, you can see the apache, php and mysql packages being used in the list.
How did I find the cause: I tried the package installation script again and it threw these errors

The following packages have unmet dependencies:
 mysql-server : Depends: mysql-server-5.5 but it is not going to be installed
 php5-curl : Depends: php5-common (= 5.4.9-4ubuntu2) but 5.4.9-4ubuntu2.1 is to be installed
 php5-mysql : Depends: php5-common (= 5.4.9-4ubuntu2) but 5.4.9-4ubuntu2.1 is to be installed
E: Unable to correct problems, you have held broken packages.

Then I Googled the first line (mysql) and found the askUbuntu answer page.
This indicated the cause to be a recent addition of and external repo into my repo list.
How did I fix the problem : I first removed repos that were added by me from Synaptic > Other softwares. [ Open Synaptic and then untick repos from "Other software" tab
First I executed the commands

sudo apt-get -f remove mysql-server-core-5.5 mysql-server-5.5 mysql-server-5.5 mysql-server
sudo apt-get -f remove php5-curl
sudo apt-get -f remove php5-common

Then executed the installation commands again and the problem was fixed.