Here is a HTML rendition of the notes for a short course on ADQL and TAP.
It’s allowed to cut-and-paste the queries…
Also, there’s a PDF version that you can print and keep as a makeshift reference.
The queries and problems in the text are supposed to be run against the server ivo://uni-heidelberg.de/gaia/tap with the access URL http://gaia.ari.uni-heidelberg.de/tap (unless something else is specified).