Which database to choose relational or NoSQL?

Question

MySQL

There are several companies that share customer data.
It is necessary to organize a decentralized distributed system for storing customer data.
there are the following requirements
Organize a single secure automated platform for information exchange between subjects in accordance with the available modern requirements and technologies.
The main requirement for the structure of the solution is decentralization, that is, the absence of a dedicated “center” that aggregates and manages the collected information.
system requirements.
Working with the database The
possibility of presenting data to the user on request (search for information) should be implemented.
The possibility of adding (changing) data (replenishing the database) should be implemented
• adding cards "one at a time"
• batch adding
• when adding data, it should be possible to identify a previously created card
When adding data, it should be possible to expand cards with additional fields
• the ability to select added field from previously fixed additional fields
• the ability to add new additional fields with fixing the following information:
o field identifier (unique among all possible fields of the card)
o field name (used when building a GUI)
What is the best and most convenient way to organize this?

Answer 1

each company keeps a copy of the database and adds to it

No. The repository must be centralized. But how it is arranged by itself is another matter, and here it is already necessary to proceed from the scale.