If you used the new RASPBIAN STRETCH OS 2017-09-07 for your Raspberry PI (Debian Stretch from www.raspberrypi.org/downloads/) you need to install MySQL like I have done in this video.

To store data from your differed sensors it is the best to store it in a database like MySQL

The password for the mysql it the password you set when it ask you during the install of phpmyadmin.

This is the password you use it again when you call “mysql -u root -p” and you can change the password on this position.

I know, I know…. I used a very stupid password ‘test’ 😉
or change it here:

GRANT ALL PRIVILEGES on *.* to ‘root’@’localhost’ IDENTIFIED BY ‘your password’;