Start to finish... a long, long time. 18 months on and off, 4 months full time. I started this before I was employed at PlanetScale and when I joined PS the course came along with me. I wouldn't have had the space to do it if it hadn't been my full time job. For the past four months or so I've been spending 100% of my work time on it, and much of my spare time.
Part of what made it tough is that, while I've been comfortable with MySQL for a long time, _teaching_ it is a whole different thing. So I ended up having to study a _ton_. Lots and lots of videos trashed when I got to a point of explaining something and realized I didn't know it well enough to teach. Back to the docs to figure it out myself and then back to recording.
I could do it again in about 1/3rd the time, but of course I could! I've done all the hard parts now! The actual recording and editing was of course hard, but the up front work to make sure I wasn't making stuff up was probably the biggest slog of it all.
I've taught courses on SQL to newbies and learned a lot from it.
My rule for the slide deck was "don't use a term you haven't explained". So I'd write a slide and check for new words. If I really needed them I'd have to add a slide before that introduced and explained the term.
Figuring out exercises that got students oriented to the concepts was another trick. People really don't get stuff until they've done it for themselves.
By the end of the second day I had people writing joins on their own.
