How to solve "Extension mysqli | mysql not found"

I noticed once on one of the new Ubuntu servers an error when opening phpMyAdmin – “The extension mysqli | mysql not found.”

It is solved simply by installing the extension with the following command:

sudo apt-get install php5-mysql

Or:

sudo apt install php-mysql

Then we restart the web server to apply the changes:

sudo service apache2 restart

Done.

How to solve “Extension mysqli | mysql not found”