Author here: yeah, that seems to be a common theme. I will probably update the site at some point to fix this. Sadly I'm mid-emigration at the moment, so it probably won't be in the immediate future :-). I've raised https://github.com/AlisdairO/pgexercises/issues/19 to cover it so I don't forget.
Your site looks great! I built https://www.sqlteaching.com , so feel free to use that design if you want a setup that has both the schema and expected output. I made the design tradeoff of using really small datasets.
