FWIW I created flashcards on the stuff (no pun intended) I learned, but I am having trouble retaining the info I learned since I don't require that type of complexity in my queries very often. I do have a Google Doc w/ the key notes, so I will reference that if an opportunity provides itself.That's and window functions are the two things in SQL, I haven't mastered yet. But with respect to FOR XML/STUFF, you know that SQL Server 2016 released some new string functions. They should help ease string manipulation. And I just found out there's a FOR JSON too. But I haven't used it at all.
On a related note, I'm having the complete opposite experience with Pandas (via Python). It's to the point where I have replaced the step of copy/pasting the data into Excel -> saving a CSV and loading into JupyterLab.
I was lit at an office party yesterday telling my boss' boss that we should probably try and pivot all the new hires to get more proficient in Pandas over Excel. Excel is a powerful tool, but in terms of replicating results, it's a shytshow. There have been plenty of times when I'd do +2 hours of hard work to reach the right answer to a data question, but it ends up being incorrect because of user-error like a formulae not going all the way down, the workbook calculations were set to manually update, I pasted the data off by one column inadvertently, etc.
With Pandas, it is much easier to get summary data, and more importantly, to explore the data and tease out more in-depth stories. And I say this as someone who is only like a third of the way through a course on Pandas. Even if you are a wizard in Excel, I strongly encourage you to get your Python/Pandas game up to do even more w/ less work