sqlite> select date(CURRENT_TIMESTAMP, 'localtime');
2013-01-19
sqlite> select date(CURRENT_TIMESTAMP, 'localtime', 'start of month', '-1 month');
2012-12-01
sqlite> select date(CURRENT_TIMESTAMP, 'localtime', 'start of month', '-1 day');
2012-12-31
CURRENT_TIMESTAMPは変えとけよ