Обсуждение: BUG #7498: Questionable interval parsing when in the form 'n m days'

The following bug has been logged on the website:

Bug reference:      7498
Logged by:          Daniel Farina
Email address:      daniel@heroku.com
PostgreSQL version: 9.1.4
Operating system:   Ubuntu 12.04
Description:        =


This is an expression that should probably have an error and not evaluate to
"true":

select '1 5 hours'::interval =3D '1 day 5 hours'::interval;
 ?column? =

----------
 t
(1 row)

I think that the first spelling, a unit-less '1', should not be accepted. =

Other unit combinations agree:

select '1 5 minutes'::interval;
ERROR:  invalid input syntax for type interval: "1 5 minutes"
LINE 1: select '1 5 minutes'::interval;
               ^
select '1 5 months'::interval;
ERROR:  invalid input syntax for type interval: "1 5 months"
LINE 1: select '1 5 months'::interval;
               ^
select '1 5 seconds'::interval;
ERROR:  invalid input syntax for type interval: "1 5 seconds"
LINE 1: select '1 5 seconds'::interval;

daniel@heroku.com writes:
> select '1 5 hours'::interval = '1 day 5 hours'::interval;
>  ?column?
> ----------
>  t
> (1 row)

> I think that the first spelling, a unit-less '1', should not be accepted.

Not sure I agree.  The syntax '1 05:00' is required by spec to mean
'1 day 5 hours 0 minutes'.  I would take that to mean that a unitless
number directly to the left of an hours field is days.  Anyway, the
code in DecodeInterval is treating these cases the same.

            regards, tom lane

On Wed, Aug 15, 2012 at 5:19 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> daniel@heroku.com writes:
>> select '1 5 hours'::interval = '1 day 5 hours'::interval;
>>  ?column?
>> ----------
>>  t
>> (1 row)
>
>> I think that the first spelling, a unit-less '1', should not be accepted.
>
> Not sure I agree.  The syntax '1 05:00' is required by spec to mean
> '1 day 5 hours 0 minutes'.  I would take that to mean that a unitless
> number directly to the left of an hours field is days.  Anyway, the
> code in DecodeInterval is treating these cases the same.

Interesting. I see your point, but I think that a user writing a
symbolic name of the unit is probably different than the one relying
on '1 05:00'.  My reasoning is that without any units specified that
what one has is a syntax that is contingent on position, whereas the
symbolic units are not:

  select '3 minute 1 day'::interval = '1 day 3 minute'::interval;

And I think that's why '1 5 hours' is funny looking vs '1 5:00', borne
out more by the confusion as to why 'hours' is given this special
status but any other unit that I have tried is not.  It also reads
much closer to "15 hours" than "1 5:00" does in my opinion.

I am hard pressed to imagine a person who would prefer the 'M N hours'
variant of the notation be accepted, but  perhaps that is more of a
general problem with the positional syntax...consider:

    select '1 5:'::interval = '1 day 5 hours'::interval;

Whereby the valid interval string is "1 5:".

--
fdr