How to protect database data?

Question

Data protection

Hello everyone, tell me please, I’m interested in such a question - there is a site that is less than a year old and has not been promoted in any search engines or anywhere else (that is, it is very difficult to find it that it exists at all). Recently, I lost data from the database in some tables, as a result, the site was broken and it did not function (the backend worked, the frontend did not). I used to be interested in hacks too and found an interesting article about the fact that you can add your own to the request and thus delete all data (very suitable for this case). There is also a simple username/password pair.
The question is: could they come to my site and thus hack, given what I described above or not?
Question 2: how to protect yourself from such cases so that they cannot delete data in the database?
And will it be enough that I change the password \ login? Any advice would be greatly appreciated as this is my first experience with this.

Answer 1

1. Yes, and not only in this way.
2. Filter data using regex used in queries to the database.
3. How to protect websites from hacking?

Answer 2

See logs. Without logs - fortune-telling on the coffee grounds.