Here is a HTML rendition of the notes for a short course on ADQL and TAP. All queries follow the ADQL standard 2.1 as defined by the IVOA at http://www.ivoa.net/documents/ADQL/20180112/PR-ADQL-2.1-20180112.pdf
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://org.gavo.dc/__system__/tap/run with the access URL http://dc.g-vo.org/tap (unless something else is specified).