Installing php7.4 + MySql on Stretch with nginx

Question

I want OwnCloud and I am trying to install PHP 7.4 on Raspbian GNU/Linux 9 (stretch) following @janw's tutorial but facing some errors:

1. E: Unable to locate package php7.4-… then I was able to solve this with sudo sh -c 'echo "deb http://ftp.us.debian.org/debian sid main " > /etc/apt/sources.list' and sudo apt-get update && sudo apt-get upgrade libc6.
2. Then mysql: command not found was my next error. After sudo apt install mysql-client and sudo apt install mysql-server was the new error
3. ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' and no luck with any of these: ubuntu - ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysql.sock'

Anyone have any other idea to make it work?