I'm an engineer on the Mathesar core team and I'd just like to clarify that Mathesar does support grouping to some extent. Here is a screenshot[1] that demonstrates the grouping functionality. Grouping levels are unlimited. You can play with this functionality on our live demo[2]. It's worth mentioning that Mathesar does not yet have the capability to expand and collapse groups, but that feature is planned[3].
Best of luck building Visual DB! Nice to see more innovation in this space!
Good question. We've taken a somewhat unique approach of integrating tightly with PostgreSQL in order to leverage its strengths. In the short term, we plan to continue with this focus on PostgreSQL, but we are considering supporting other DBs in the long term. Thanks for your comment though! Knowing that you have an interest in using Mathesar with MySQL is a useful data point for us!
