Craft Internal Server Error
I have tried the methods answered in this similar question:

Getting this SQL Error: GROUP BY incompatible with sql_mode=only_full_group_by

To fix my issue all I did was edit this file:

nano /etc/my.cnf


with the following line:

sql_mode="NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES"


The website was back up and running instantly.