I am working on a mobile/web app like Instagram. Considering that, I want to know for what part of the app it's better to use relational and for what other parts non-relational databases. I have chosen MySQL and Cassandra databases and this is my research result so far: -Relational Databases: - For services we need as much as possible consistency like payment service or ordering and authentication services. - Non-relational Databases: - For services we need to summarize a lot of different data in a small table instead of a lot of columns with null values, like user services that we have a lot of personal settings. - For the time we need horizontal scalability and want more distributed system over different datacenters/clouds. - For faster read/write heavy systems. But I am still wondering to know: 1- What database is more appropriate for upload files(images, videos. documents) on it? 2- What database is more sufficient for posts/comments/likes, list of friends, and other user related things that they are also related to other users. (***I mean a post or a comment is related to one user but all the other users can also see it, and may affect them***).

I'll begin by saying I am new to DynamoDB and the world of NoSQL in general. I have a patient entity and I am storing it in a DynamoDB table. My access patterns for the patient entity are: 1. Get patient by id 2. Get patient by first name 3. Get patient by last name 4. Get patient by date of birth 5. Get patient by post code How can I achieve this with my DynamoDB table? Right now, the basic model I've put together is: I'm still in the data modelling phase, so I can ditch that make as many changes as I want.