The following bug has been logged online:
Bug reference: 4702
Logged by: Roman Kononov
Email address: kononov(at)ftml(dot)net
PostgreSQL version: 8.3.6 and older
Operating system: GNU/Linux x86_64
Description: refusal to compute date_trunc('week', '0001-12-09 BC');
Details:
test=# select date_trunc('week','0001-12-09 BC'::timestamp);
ERROR: cannot calculate week number without year information