General developer forum

Well the 1.9 documentation is here http://docs.moodle.org/19/en/Main_Page and in fact on the main page of the current documentation it links to older versions

http://docs.moodle.org/22/en/Main_page but I am not sure what you mean by database API so sorry I can't help you search more

http://docs.moodle.org/dev/DML_functions_-_pre_2.0

You will find the old Database FAQ for Moodle 1.9 at http://docs.moodle.org/19/en/Database_FAQ (which I compiled some time ago). I haven't checked whether all the links are still valid (I fear not).

Unfortunately, the new cloning concept for Moodle Docs (where each version gets its own wiki) - which IMHO is already bad enough - doesn't extend to the Developer Documentation where you will only find information on the most current version of Moodle.

There are several threads in the Moodle Docs forum relating to that topic. The most recent one is "Performance docs in a mess". Please comment there if you want to change this pity state of Moodle Docs.

Cheers,
Frank

The best documentation is the PHPdocs, so look in lib/dmllib.php (assuming you don't want to run PHPdoc to compile them into HTML)