If your default programming language, like mine, is Java, you most likely wince at the very thought of date arithmetic. (It’s changed for the better with Java 8 but Vertabelo is not there yet.)
The date arithmetic API in PostgreSQL is like a breath of fresh air.
You can represent a time interval:
select interval '2 days'; '2 days'
select interval '3 hours'; 03:00:00
select interval '5 weeks'; '35 days'
Add an interval to a date or subtract an interval from a date:
select current_timestamp; 2014-05-12 12:44:45.97619
select current_timestamp – interval '2 hours'; 2014-05-12 10:44:45.97619
select current_timestamp + interval '5 days'; 2014-05-17 12:44:45.97619
You can truncate dates to the specified precision.
select date_trunc('hour', current_timestamp); 2014-05-12 12:00:00.0
select date_trunc('day', current_timestamp); 2014-05-12 00:00:00.0
... including fancy precisions like week (returns the beginning of Monday)
select date_trunc('week', current_timestamp); 2014-05-12 00:00:00.0
... or month precision (midnight on the first day of the month):
select date_trunc('month', current_timestamp); 2014-05-01 00:00:00.0
How cool is that?