I need to add a useful column, so that it would be easy to me to create a web script which would display today's and all past "daily puzzle" records - and wouldn't change the already published puzzles...
Serial (i.e. integer/bigint with an sequence generator). I would then add another table that simply stores the "last manually reviewed id" as its only record (or you could record manual reviews and take the max of that field from the table).
