A short course on the VO's SQL-like query language, the Astronomical
Data Query Language. It also covers basic operation of some TAP user
agents. It is available as a multipage HTML rendering for online
perusal as well as a one-file PDF.
GAVO's ADQL reference card briefly gives an overview of the SQL
dialect used in the VO. It is available as a PDFfile and as Scribus
source under the CC-BY license.