Hi @Akoto_Christopher and welcome to the community 
I’m not working for Mozilla or other organizations involved in MDN Web Docs and therefore I don’t know there plans. This is just my view as a volunteer on this forum.
The main purpose of MDN is to document technologies used in browsers. So it seems natural that the learning area also focuses on this topics. That being said with Server-side website programming there is already a learning path looking at back-end technologies. Maybe this will get extended in the future to also cover database interactions.
As many others I am working on front-end and back-end development and understand your request for SQL being included in the learning area. 
Michael