Which one would you recommend to use in a mobile app, SQL Server or MongoDB?

Question

Data bases applied to mobile applications for Android and iOS.

Answer 1

From technical perspective it doesn't matter, because these database engines will not run on a mobile device. They can run on a web server as back-end, and the mobile app can communicate with it.
Whether you use a relational database or a NOSQL choice such as Mongo, really depends on the requirements of the particular application. SQL and NOSQL have different advantages and weaknesses. Some apps could be implemented with either choice.

Answer 2

If your database doesn’t need to communicate with the backend by design, such as playlist, most played song, etc. storing locally, then sqlite would be a good choice.

Answer 3

It depends on the kind of data you're working with.

Are you working with a lot of *structured* data like user information, account activity, messages, etc.? Use a *structured* database like MySQL.

Are you working with mostly *unstructured* data like songs, videos, and images? Are you hosting and streaming large quantities of content that isn't text or numerical based? Probably better to work with an *unstructured* database like MongoDB.

If you're working with a mix of data, use two databases and develop a good schema, architecture, and API.