Pretty much the only document is the ASQL Reference on the
A-Shell Documents page.
The 6.4 Linux bin packages contain the libashmysql connector library.
Beyond that, you'll want to play with the SQLTEST# programs in the SQL: directory - typically [909,60]. There has been some confusion over how that has been distributed, so if you don't have it, let me know and I'll zip up a copy and email it to you.