The database’s structure used to be documented by AnkiDroid at: https://github.com/ankidroid/Anki-Android/wiki/Database-Structure (and not by the main Anki project, as far as I’m aware).
It looks like the database schema has changed completely (somewhere between 2.1.13 and 2.1.28, i.e. on a “patch version”?): for instance, “SELECT decks FROM col” doesn’t return a JSON containing information about the decks anymore, but an error. Instead, the information seems to be in a “decks” table.
Is this documented anywhere? If it is, it doesn’t look like Google has noticed it, and I couldn’t find it in the manual