Most tutorials pick a non-relational database or a document-oriented database, like Mongo. Hardly any tutorials I stumble across ever use a relational DB for a full-stack tutorial. It may be partially because it's a tutorial, and the tutorials I see are mostly invested in everything besides how the data is stored...
Adam Bene
Founder & CTO @ Bene Studio | Join us!
If you have table based data with a lot of relations than an RDMS suits well the task. RDMSs can manage foreign keys and cascade records on delete for you. Usually RDMSs can be scaled well for read but not for write out of the box.
If you have less relations or the structure needs to be flexible then go with document based DBs. However you have to manage any relations and remove related unnecessary records on delete. Watch out for the NoSQL hype, analyse your situation. They usually can be scaled for write and read as well.
Other NoSQL databases such as Redis are perfect for key-value caching.