I'm a newbie on MySQL ground so bear with me.

I've just finished upgrading 11.10 to 12.04.

Everything seemed to work without any hiccups and all my software and settings are working fine. Apart from MySQL.

When I try:

sudo start mysql

I receive an error:

start: Job failed to start

Where can I possibly diagnose what the problem is? And (hopefully) - how to sort it out?

(I disabled automatic start following advice here if that is of some importance)

Update 1:

Both outputs of:

cat /var/log/mysql.err 
cat /var/log/mysql.log

are empty.

Output of dmesg | grep mysql:

[ 1401.785141] type=1400 audit(1335619832.181:25): apparmor="STATUS" operation="profile_replace" name="/usr/sbin/mysqld" pid=16165 comm="apparmor_parser"
[ 1401.791089] init: Failed to spawn mysql main process: unable to execute: No such file or directory

Update 2:

As indicated by AWinter below - it seemed that MySQL disappeared automagically after upgrade and had to be reinstalled.