Re: [BUGS] BUG #3431: age() gets the days wrong - Mailing list pgsql-hackers

Sorry, I see there was later discussion.

---------------------------------------------------------------------------

Tom Lane wrote:
> "Pelle Johansson" <pelle@morth.org> writes:
> > The age() function seem to work by first counting months until less than a
> > month remains to to the second argument, then counting days left. This
> > doesn't give the correct result, as shown by this example:
> 
> > # select column1, age(column1, '2006-11-02'), date '2006-11-02' +
> > age(column1, '2006-11-02') from (values ('2007-01-31'::date),
> > ('2007-02-01')) as alias;
> >   column1   |      age       |      ?column?       
> > ------------+----------------+---------------------
> >  2007-01-31 | 2 mons 29 days | 2007-01-31 00:00:00
> >  2007-02-01 | 2 mons 29 days | 2007-01-31 00:00:00
> > (2 rows)
> 
> I took another look at this example.  I believe what is actually going
> wrong here is that when timestamp_age converts a month into an
> equivalent number of days, it uses the number of days in the first
> month of the interval it's dealing with (ie, the month containing
> the earlier of the two dates).  This is just wrong, because interval
> addition adds months first and then days.  The appropriate conversion
> to use is actually the length of the next-to-last month of the interval.
> 
> As an example, 8.2 and CVS HEAD produce
> 
> regression=# select age('2007-03-14', '2007-02-15');
>    age   
> ---------
>  27 days
> (1 row)
> 
> which is reasonable, but
> 
> regression=# select age('2007-04-14', '2007-02-15');
>       age      
> ---------------
>  1 mon 27 days
> (1 row)
> 
> is not so reasonable, nor is
> 
> regression=# select age('2007-03-14', '2007-01-15');
>       age      
> ---------------
>  1 mon 30 days
> (1 row)
> 
> If we change the code to use the next-to-last month of the interval
> then these two cases produce '1 mon 30 days' and '1 mon 27 days'
> respectively.
> 
> Another problem is that the code isn't doing the propagate-to-next-field
> bit for negative fractional seconds.  Hence it produces
> 
> regression=# select age('2007-02-14 01:00:00', '2007-01-15 01:00:00.4');
>          age          
> ----------------------
>  30 days -00:00:00.40
> (1 row)
> 
> which is maybe not incorrect, but certainly fairly inconsistent with
> 
> regression=# select age('2007-02-14 01:00:00', '2007-01-15 01:00:01');
>        age        
> ------------------
>  29 days 23:59:59
> (1 row)
> 
> 
> Hence I propose the attached patch.  This does not change any existing
> regression test outputs, but it does change the example given in the
> documentation: age(timestamp '2001-04-10', timestamp '1957-06-13')
> will now produce '43 years 9 mons 28 days' not 27 days.  Which actually
> is correct if you try to add back the result to timestamp '1957-06-13'.
> It also appears to fix Palle's example:
> 
> regression=# select column1, age(column1, '2006-11-02'), date '2006-11-02' +
> age(column1, '2006-11-02') from (values ('2007-01-31'::date),
> ('2007-02-01')) as alias;
>   column1   |      age       |      ?column?       
> ------------+----------------+---------------------
>  2007-01-31 | 2 mons 29 days | 2007-01-31 00:00:00
>  2007-02-01 | 2 mons 30 days | 2007-02-01 00:00:00
> (2 rows)
> 
> As I said earlier, I'm worried about changing the behavior of a function
> that's been around for so long, so I'm disinclined to back-patch this.
> But it seems like a reasonable change to make in 8.3.  Comments?
> 
>             regards, tom lane
> 

Content-Description: age.patch

> Index: timestamp.c
> ===================================================================
> RCS file: /cvsroot/pgsql/src/backend/utils/adt/timestamp.c,v
> retrieving revision 1.179
> diff -c -r1.179 timestamp.c
> *** timestamp.c    6 Jul 2007 04:15:59 -0000    1.179
> --- timestamp.c    8 Jul 2007 19:45:04 -0000
> ***************
> *** 3044,3050 ****
>       if (timestamp2tm(dt1, NULL, tm1, &fsec1, NULL, NULL) == 0 &&
>           timestamp2tm(dt2, NULL, tm2, &fsec2, NULL, NULL) == 0)
>       {
> !         fsec = (fsec1 - fsec2);
>           tm->tm_sec = tm1->tm_sec - tm2->tm_sec;
>           tm->tm_min = tm1->tm_min - tm2->tm_min;
>           tm->tm_hour = tm1->tm_hour - tm2->tm_hour;
> --- 3044,3051 ----
>       if (timestamp2tm(dt1, NULL, tm1, &fsec1, NULL, NULL) == 0 &&
>           timestamp2tm(dt2, NULL, tm2, &fsec2, NULL, NULL) == 0)
>       {
> !         /* form the symbolic difference */
> !         fsec = fsec1 - fsec2;
>           tm->tm_sec = tm1->tm_sec - tm2->tm_sec;
>           tm->tm_min = tm1->tm_min - tm2->tm_min;
>           tm->tm_hour = tm1->tm_hour - tm2->tm_hour;
> ***************
> *** 3064,3069 ****
> --- 3065,3081 ----
>               tm->tm_year = -tm->tm_year;
>           }
>   
> +         /* propagate any negative fields into the next higher field */
> +         while (fsec < 0)
> +         {
> + #ifdef HAVE_INT64_TIMESTAMP
> +             fsec += USECS_PER_SEC;
> + #else
> +             fsec += 1.0;
> + #endif
> +             tm->tm_sec--;
> +         }
> + 
>           while (tm->tm_sec < 0)
>           {
>               tm->tm_sec += SECS_PER_MINUTE;
> ***************
> *** 3082,3097 ****
>               tm->tm_mday--;
>           }
>   
> !         while (tm->tm_mday < 0)
>           {
>               if (dt1 < dt2)
>               {
> !                 tm->tm_mday += day_tab[isleap(tm1->tm_year)][tm1->tm_mon - 1];
> !                 tm->tm_mon--;
>               }
>               else
>               {
> !                 tm->tm_mday += day_tab[isleap(tm2->tm_year)][tm2->tm_mon - 1];
>                   tm->tm_mon--;
>               }
>           }
> --- 3094,3130 ----
>               tm->tm_mday--;
>           }
>   
> !         /*
> !          * day-to-month conversion is tricky because variable.  For each
> !          * decrement in tm_mon, we should adjust tm_mday by the length of
> !          * the next-to-last month(s) of the original time interval.
> !          * This corresponds to the notion that interval addition will add
> !          * months first, then days.
> !          */
> !         if (tm->tm_mday < 0)
>           {
> +             int        end_year;
> +             int        end_mon;
> + 
>               if (dt1 < dt2)
>               {
> !                 end_year = tm2->tm_year;
> !                 end_mon = tm2->tm_mon;
>               }
>               else
>               {
> !                 end_year = tm1->tm_year;
> !                 end_mon = tm1->tm_mon;
> !             }
> ! 
> !             while (tm->tm_mday < 0)
> !             {
> !                 if (--end_mon <= 0)
> !                 {
> !                     end_mon = MONTHS_PER_YEAR;
> !                     end_year--;
> !                 }
> !                 tm->tm_mday += day_tab[isleap(end_year)][end_mon - 1];
>                   tm->tm_mon--;
>               }
>           }
> ***************
> *** 3158,3163 ****
> --- 3191,3197 ----
>       if (timestamp2tm(dt1, &tz1, tm1, &fsec1, &tzn, NULL) == 0 &&
>           timestamp2tm(dt2, &tz2, tm2, &fsec2, &tzn, NULL) == 0)
>       {
> +         /* form the symbolic difference */
>           fsec = fsec1 - fsec2;
>           tm->tm_sec = tm1->tm_sec - tm2->tm_sec;
>           tm->tm_min = tm1->tm_min - tm2->tm_min;
> ***************
> *** 3178,3183 ****
> --- 3212,3228 ----
>               tm->tm_year = -tm->tm_year;
>           }
>   
> +         /* propagate any negative fields into the next higher field */
> +         while (fsec < 0)
> +         {
> + #ifdef HAVE_INT64_TIMESTAMP
> +             fsec += USECS_PER_SEC;
> + #else
> +             fsec += 1.0;
> + #endif
> +             tm->tm_sec--;
> +         }
> + 
>           while (tm->tm_sec < 0)
>           {
>               tm->tm_sec += SECS_PER_MINUTE;
> ***************
> *** 3196,3211 ****
>               tm->tm_mday--;
>           }
>   
> !         while (tm->tm_mday < 0)
>           {
>               if (dt1 < dt2)
>               {
> !                 tm->tm_mday += day_tab[isleap(tm1->tm_year)][tm1->tm_mon - 1];
> !                 tm->tm_mon--;
>               }
>               else
>               {
> !                 tm->tm_mday += day_tab[isleap(tm2->tm_year)][tm2->tm_mon - 1];
>                   tm->tm_mon--;
>               }
>           }
> --- 3241,3277 ----
>               tm->tm_mday--;
>           }
>   
> !         /*
> !          * day-to-month conversion is tricky because variable.  For each
> !          * decrement in tm_mon, we should adjust tm_mday by the length of
> !          * the next-to-last month(s) of the original time interval.
> !          * This corresponds to the notion that interval addition will add
> !          * months first, then days.
> !          */
> !         if (tm->tm_mday < 0)
>           {
> +             int        end_year;
> +             int        end_mon;
> + 
>               if (dt1 < dt2)
>               {
> !                 end_year = tm2->tm_year;
> !                 end_mon = tm2->tm_mon;
>               }
>               else
>               {
> !                 end_year = tm1->tm_year;
> !                 end_mon = tm1->tm_mon;
> !             }
> ! 
> !             while (tm->tm_mday < 0)
> !             {
> !                 if (--end_mon <= 0)
> !                 {
> !                     end_mon = MONTHS_PER_YEAR;
> !                     end_year--;
> !                 }
> !                 tm->tm_mday += day_tab[isleap(end_year)][end_mon - 1];
>                   tm->tm_mon--;
>               }
>           }

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