11.0.3 - Database problem after system upgrade with apt

Hi all,
I’m using nextcloud for 2 weeks now and I’m quite satisfied, thanks for the good work!

Today I’m facing a problem. After upgrading the system using apt (armbian on Bananapi) I can’t connect to nextcloud, namely the database anymore. Some googling revealed solutions that probably only apply to older versions. Apache and MySQL seem to run. When I try to open the webpage it’s just plain blank. The error repeated error-message from apache-error.log is:

Mon May 22 00:26:57.625028 2017] [:error] [pid 987] [client xx.xx.48.221:50659] PHP Fatal error: Uncaught > Doctrine\\DBAL\\DBALException: Failed to connect to the database: An exception occured in driver: SQLSTATE[HY000] [2002] No such file or directory in /var/www/nextcloud/lib/private/DB/Connection.php:60\nStack trace:\n#0 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(429): OC\\DB\\Connection->connect()\n#1 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(389): Doctrine\\DBAL\\Connection->getDatabasePlatformVersion()\n#2 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(328): Doctrine\\DBAL\\Connection->detectDatabasePlatform()\n#3 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/Connection.php(621): Doctrine\\DBAL\\Connection->getDatabasePlatform()\n#4 /var/www/nextcloud/lib/private/DB/Connection.php(147): Doctrine\\DBAL\\Connection->setTransactionIsolation(2)\n#5 /var/www/nextcloud/3rdparty/doctrine/dbal/lib/Doctrine/DBAL/DriverManager.php(172): OC\\DB\\Connection->__construct(Array, Object(Doctrine\\DBAL\\Driver\\PDOMySql\\Driver), Obj in /var/www/nextcloud/lib/private/DB/Connection.php on line 60

Thanks in advance for your help and best regards, Olli.

[SOLVED] Since MySQL was not running (service mysql status => active.exited) I focused on this. When I checked what components were installed (dpkg-query - l ‘mysql*’) I got a bunch of concurrent versions.
So I decided to remove and reinstall - but apt-get (-f) wasn’t able to solve the problem.
In the end I used aptitude what offers to me to remove some mysql-components and upgraded my system to a consistent state.
sudo aptitude install mysql-server mysql-common
sudo aptitude upgrade
The content of my nextcloud-database was left untouched.