Re: BUG #7797: datetime + '1 month'::interval is going outside of a month's bounds

On Mon, Jan 01/07/13, 2013 at 05:42:40PM +0000, Daniele Varrazzo wrote:
> On Mon, Jan 7, 2013 at 5:19 PM, Ryan Kelly <rpkelly22(at)gmail(dot)com> wrote:
>
> > '1 month'::interval is the same as '30 days'::interval.
>
> No, it's not.
>
> # select '2012-07-31'::date + '1 month'::interval, '2012-07-31'::date
> + '30 days'::interval;
> ?column? | ?column?
> ---------------------+---------------------
> 2012-08-31 00:00:00 | 2012-08-30 00:00:00
>
> -- Daniele

Alright, now I'm thoroughly confused. What magic makes this true:

# select '30 days'::interval = '1 month'::interval;
?column?
----------
t

But not this:

# select '2012-07-31'::timestamp + '1 month'::interval = '2012-07-31'::timestamp + '30 days'::interval;
?column?
----------
f

?

-Ryan Kelly