Which database to choose for a cross-platform project?

Question

Database

Is there a universal database that is easy to work with both for developing a website and for mobile applications running ios / android? For example, for developing web sites, php developers usually use mySQL, ios developers use SQLite in their projects, andriod developers, in turn, also use some kind of database of their own. What solution should you use today if you are going to create a website and in parallel a client for mobile platforms?

Answer 1

Base - any.
Data exchange format - RESTfull API
Transfer format - JSON
Client format - SPA
(the above is true for the website and for any applications for any OS)

Answer 2

I suppose the mobile client, being an online application, will still exchange data with the backend via the API. It would be logical for a mobile client to find a ready-made library that already knows how to exchange data with the API and implement it on the API backend in exactly the way the library needs. Then golovnyakov minimum. I suppose it will be something like a RESTful API, as it was written in the first comment.
In general, the question of choosing a database comes down to the question of goals, requirements, scope, qualifications, etc.
As for SQLite, as far as I know, it is used as a local storage.