How to safely store users personal details?

Hi guys, I am new to encryption and safety standards so wanted to ask here what the best method would be to safely secure details such as address, contact details etc.

I want the data to be stored in such a way where even the root user of the database cannot decrypt the data. I was thinking each user would need their own private key, but what’s stopping the root user from being able to access this key to decrypt the data?

Apologies if this is explained poorly as I am new to the concept of encryption.