Re: [BUGS] BUG #1563: wrong week returnded by date_trunc('week', - Mailing list pgsql-patches

Robert Creager wrote:
-- Start of PGP signed section.
> When grilled further on (Tue, 29 Mar 2005 07:43:53 +0200),
> Dirk Raetzel <d00273@spaetzle.de> confessed:
>
> >
> >
> > On Mon, 28 Mar 2005, Bruce Momjian wrote:
> >
> > > I have developed a patch to fix the problem.  Instead of changing the
> > > API, I added code to decrement the year when the week number was 53 and
> > > the month was January.  It corrected the problem:
> >
> > The problem arises as well when week number is 52 as in '2006-01-01'.
>
> Try these at the least:
>
> select date_trunc_week( '2004-01-01' ); -- should be 2003-12-29 00:00:00
> select date_trunc_week( '2005-01-01' ); -- should be 2004-12-27 00:00:00
> select date_trunc_week( '2005-06-01' ); -- should be 2005-05-30 00:00:00
> select date_trunc_week( '2006-01-01' ); -- should be 2005-12-26 00:00:00
> select date_trunc_week( '2007-01-01' ); -- should be 2007-01-01 00:00:00
>
> If it helps, look earlier in this thread for a (overly complicated?) version in
> plpgsql.

Wow, an early January date can be part of the 52nd week of the previous
year too.

Here is a new patch, with a documentation mention.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
Index: doc/src/sgml/func.sgml
===================================================================
RCS file: /cvsroot/pgsql/doc/src/sgml/func.sgml,v
retrieving revision 1.242
diff -c -c -r1.242 func.sgml
*** doc/src/sgml/func.sgml    25 Mar 2005 16:08:39 -0000    1.242
--- doc/src/sgml/func.sgml    30 Mar 2005 06:04:39 -0000
***************
*** 5472,5477 ****
--- 5472,5483 ----
          week starts on Monday.)  In other words, the first Thursday of
          a year is in week 1 of that year. (for <type>timestamp</type> values only)
         </para>
+        <para>
+         Because of this, it is possible for early January dates to be part of the
+         52nd or 53rd week of the previous year.  For example, <literal>2005-01-01</>
+         is part of the 53rd week of year 2004, and <literal>2006-01-01</> is part of
+         the 52nd week of year 2005.
+        </para>

  <screen>
  SELECT EXTRACT(WEEK FROM TIMESTAMP '2001-02-16 20:38:40');
Index: src/backend/utils/adt/timestamp.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/utils/adt/timestamp.c,v
retrieving revision 1.117
diff -c -c -r1.117 timestamp.c
*** src/backend/utils/adt/timestamp.c    31 Dec 2004 22:01:22 -0000    1.117
--- src/backend/utils/adt/timestamp.c    30 Mar 2005 06:04:41 -0000
***************
*** 2754,2765 ****
          switch (val)
          {
              case DTK_WEEK:
!                 isoweek2date(date2isoweek(tm->tm_year, tm->tm_mon, tm->tm_mday), &(tm->tm_year), &(tm->tm_mon),
&(tm->tm_mday));
                  tm->tm_hour = 0;
                  tm->tm_min = 0;
                  tm->tm_sec = 0;
                  fsec = 0;
                  break;
              case DTK_MILLENNIUM:
                  /* see comments in timestamptz_trunc */
                  if (tm->tm_year > 0)
--- 2754,2776 ----
          switch (val)
          {
              case DTK_WEEK:
!             {
!                 int woy;
!
!                 woy = date2isoweek(tm->tm_year, tm->tm_mon, tm->tm_mday);
!                 /*
!                  *    If it is week 52/53 and the month is January,
!                  *    then the week must belong to the previous year.
!                  */
!                 if (woy >= 52 && tm->tm_mon == 1)
!                     --tm->tm_year;
!                 isoweek2date(woy, &(tm->tm_year), &(tm->tm_mon), &(tm->tm_mday));
                  tm->tm_hour = 0;
                  tm->tm_min = 0;
                  tm->tm_sec = 0;
                  fsec = 0;
                  break;
+             }
              case DTK_MILLENNIUM:
                  /* see comments in timestamptz_trunc */
                  if (tm->tm_year > 0)
***************
*** 2874,2886 ****
          switch (val)
          {
              case DTK_WEEK:
!                 isoweek2date(date2isoweek(tm->tm_year, tm->tm_mon, tm->tm_mday), &(tm->tm_year), &(tm->tm_mon),
&(tm->tm_mday));
                  tm->tm_hour = 0;
                  tm->tm_min = 0;
                  tm->tm_sec = 0;
                  fsec = 0;
                  redotz = true;
                  break;
                  /* one may consider DTK_THOUSAND and DTK_HUNDRED... */
              case DTK_MILLENNIUM:

--- 2885,2908 ----
          switch (val)
          {
              case DTK_WEEK:
!             {
!                 int woy;
!
!                 woy = date2isoweek(tm->tm_year, tm->tm_mon, tm->tm_mday);
!                 /*
!                  *    If it is week 52/53 and the month is January,
!                  *    then the week must belong to the previous year.
!                  */
!                 if (woy >= 52 && tm->tm_mon == 1)
!                     --tm->tm_year;
!                 isoweek2date(woy, &(tm->tm_year), &(tm->tm_mon), &(tm->tm_mday));
                  tm->tm_hour = 0;
                  tm->tm_min = 0;
                  tm->tm_sec = 0;
                  fsec = 0;
                  redotz = true;
                  break;
+             }
                  /* one may consider DTK_THOUSAND and DTK_HUNDRED... */
              case DTK_MILLENNIUM:

***************
*** 3142,3148 ****
       * Sometimes the last few days in a year will fall into the first week
       * of the next year, so check for this.
       */
!     if (result >= 53)
      {
          day4 = date2j(year + 1, 1, 4);

--- 3164,3170 ----
       * Sometimes the last few days in a year will fall into the first week
       * of the next year, so check for this.
       */
!     if (result >= 52)
      {
          day4 = date2j(year + 1, 1, 4);

***************
*** 3198,3204 ****
       * Sometimes the last few days in a year will fall into the first week
       * of the next year, so check for this.
       */
!     if (result >= 53)
      {
          day4 = date2j(year + 1, 1, 4);

--- 3220,3226 ----
       * Sometimes the last few days in a year will fall into the first week
       * of the next year, so check for this.
       */
!     if (result >= 52)
      {
          day4 = date2j(year + 1, 1, 4);