PostgreSQL/Date Timezone/date trunc
date_trunc("hour", now())
<source lang="sql">
postgres=# postgres=# SELECT date_trunc("hour", now());
date_trunc
2006-10-08 15:00:00-07
(1 row) postgres=# postgres=#
</source>
date_trunc("minute", now())
<source lang="sql">
postgres=# SELECT date_trunc("minute", now());
date_trunc
2006-10-08 15:12:00-07
(1 row) postgres=#
</source>
date_trunc("year", now())
<source lang="sql">
postgres=# postgres=# SELECT date_trunc("year", now());
date_trunc
2006-01-01 00:00:00-08
(1 row) postgres=#
</source>