Simple, really ... using v7.2b3 that hasn't been released yet ...
traf_stats=# select EXTRACT(WEEK FROM TIMESTAMP runtime) from hourly_stats;
ERROR: parser: parse error at or near "runtime"
traf_stats=# \d hourly_stats
Table "hourly_stats"
Column | Type | Modifiers
------------+-----------------------------+-----------
from_ip | inet |
to_ip | inet |
port | integer |
bytes | bigint |
runtime | timestamp(6) with time zone |
no_records | integer |
Indexes: hourly_from_ip,
hourly_to_ip