Re: Why 'infinity' is not in range '[2019-01-02, infinity]'?

"Jonathan S. Katz" <[email protected]> Mon, 29 Apr 2019 13:14:25 -0400
Newsgroups	gmane.comp.db.postgresql.devel.documentation
Message-ID	<[email protected]>
On 4/29/19 12:12 PM, PG Doc comments form wrote:
> The following documentation comment has been logged on the website:
> 
> Page: https://www.postgresql.org/docs/11/rangetypes.html
> Description:
> 
> Hi.
> 
> May I read this:
> 
> But [today,infinity] means something different from [today,infinity) — the
> latter excludes the special timestamp value infinity.
> 
> as 
> 
> But [today,infinity] means something different from [today,infinity) — the
> **first includes** the special timestamp value infinity.
> 
> But previous paragraph says:
> 
> But note that these infinite values are never values of the range's element
> type, and can never be part of the range. (So there is no such thing as an
> inclusive infinite bound — if you try to write one, it will automatically be
> converted to an exclusive bound.)
> 
> if 'infinity' can not be the part of a range this will mean:
> 
> [today,infinity] means same as [today,infinity)
> 
> errr... which one is correct? Please fix documentation.

'infinity' in that case is a special type of date/timestamp:

https://www.postgresql.org/docs/current/datatype-datetime.html#id-1.5.7.13.19.8

which is what that paragraph is referring to. It's discussing
"infinity-like" objects you may see that are different than how range
types treat infinity.

I re-read the language, I would not advocate for making any changes.


> PS. The problem I am faced into:
> I am implementing be-temporal interface. I have current period. It can be
> [2019-01-01,2019-02-01),
> [2019-02-01,2019-03-01) and [2019-03-01,infinity) for the current month.
> 
> When I setup current_period to one of those I will get Orders at that
> period. The Orders have with 'last_bill_date' field which will show the date
> of Invoice for that Order.
> For new Order we can set 'infinity' into 'last_bill_date' which will mean
> that we should create Invoice.
> Now to select all Order for which we should create Invoice we can write:
> 
> select * from "order" o where o.last_bill_date +interval o.bill_interval <@
> current_period();
> 
> This seems obvious that infinity is part of [value, infinity) ( or
> [value,infinity] ) range. (in other words the 'infinity' is always the part
> of range with infinite inclusive or exclusive bound.
> 
> This is just view from my point, there can be things that I am not aware of.

You should drop the 'infinity' and just let it be NULL, i.e.

daterange('2019-03-01', NULL);

Jonathan
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