Various Issues with different database backends

[JulianJacobi]

I've tried to install the software in last days and faced much difficulties with postgresql, mysql and sqlite database backends on that way.

So first of all my setup ist a virtual machine with NixOS (wich also creates some other challenges, but nothing a patch can't solve).

1. PostgreSQL: first i tried to install with PostgreSQL, all went fine, scheme creation worked, but was not able to undo transactions because of the following error in PostgreSQL:

FOR UPDATE cannot be applied to the nullable side of an outer join

2. MySQL and SQLite: Both have the same Problem, as far as i'm not executing with APP_DEBUG=true setting, i've got the following error on schema creation an in normal operation mode:

Operation 'Doctrine\DBAL\Platforms\AbstractPlatform::getCreateSequenceSQL' is not supported by platform.