If you want to make money, I recommend starting with postgres or mariadb. IME, dev shops favor those because they have the desirable characteristics of being free and not terrible. Although, again, IME, as an industry, we've been moving away from classic rdbs. Where I work, we're storing most of our data as JSON in S3 and I'm looking to move what's left in our mysql db into QLDB within the next half decade.
A neat tool to look into for reading JSON data is jq, which I use all the time at work: https://stedolan.github.io/jq/
It basically takes JSON data that your software usually manipulates, and turns it into something that you can pipe into the standard *n*x toolset.
legal disclaimer: the information offered here is my personal opinion and not the opinion of my employer