After upgrading ubuntu to 12.04 i have run into problems with mysql.
First of all, if you are going to make an upgrade of "anything", the main tip is to make a backup of the databases and files which you consider important. If you didn't, maybe you still can save something, copy your /var/lib/mysql directory. If you finally have to reinstall your mysql, loosing the databases, maybe you will be lucky and copying again /var/lib/mysql directory could give your data back.
ok, the problem with mysql 5.5 and ubuntu 12.04.
The following packages have unmet dependencies:
mysql-server : Depends: mysql-server-5.5 but it is not installed
E: Unmet dependencies. Try using -f.
Trying apt-get -f install did not solve anything. Tryied then apt-get install mysql-server-5.5
No luck, but then i saw this:
trying to overwrite '/usr/lib/mysql/plugin/ha_example.so', which is also in package libmysqlclient-dev
And the solution came to my mind: remove the conflictive package:
sudo dpkg -r libmysqlclient-dev
apt-get -f install
finally worked and did the magic. I did backups of my important databases before going to this "party", but anyway, after installing again mysql (apt-get -f intall did) everything was working fine, mysql included.
Hope it helps :-)