Ubuntu – How to enable PostgreSQL driver for PDO for php 7

Have you tried to just purge the packages left from the failed removal attempt manually?

sudo apt-get purge postgresql-client-9.4 postgresql-client-common postgresql-common

Then:

sudo apt-get update install postgresql

The removal obviously fails because postgresql is not installed, but the reinstallation might be failing because something is wrong with what has been left from the previous installation.

At this stage I would simply recommend "turning it off and on again" by doing:

sudo apt-get purge php-common php5-common

followed by

sudo rm -r /etc/php

And then reinstalling PHP 7.0 and mysql modules:

sudo apt-get install libapache2-mod-php php-mysql

You may also try just purging and reinstalling mysql modules, first removing the package:

sudo apt-get purge php7.0-mysql

And the installing them again:

sudo apt-get install php-mysql

In both cases it's important to use apt-get purge instead of apt-get remove to delete any existing configuration files and package states.

The least destructive way would be trying to re-enable mysql modules using phpenmod command:

sudo phpenmod mysqlnd pdo_mysql

It's hard to give you correct advice if we don't know what mayhem you created on your system.