Install MySQL 5.6 in Ubuntu 16.04
Ubuntu 16.04 only provides packages for MySQL 5.7 which has a range of backwards compatibility issues with code written against older MySQL versions.
Oracle maintains a list of official APT repositories for MySQL 5.6, but those repositories do not yet support Ubuntu 16.04. However, the 15.10 repos will work for 16.04.
Uninstall existing mysql 5.7 if any
sudo apt remove mysql-client mysql-server libmysqlclient-dev mysql-common