Dear Tom,

> After all that about numbering centuries and millenia correctly,
> why does CVS tip still give me
>
> regression=# select extract(century from now());
>  date_part
> -----------
>         20
> (1 row)
> [ ... looks in code ... ]
>
> Apparently it's because you fixed only timestamp_part, and not
> timestamptz_part.  I'm not too sure about what timestamp_trunc or
> timestamptz_trunc should do, but they may be wrong as well.

Sigh... as usual, what is not tested does not work:-(


> Could we have a more complete patch?

Please find a submission attached. I hope it really fixes all decade,
century and millenium issues for extract and *_trunc functions on interval
and other timestamp types. If someone could check that the results
are reasonnable, it would be great.

I indeed overlooked the fact that there were two functions. The patch
fixes the code so that both variants agree.

I added comments to interval extractions, because it relies on the C
division to have a negative remainder: -7/10 = 0 and remains -7.

As for *_trunc functions, I have chosen to put the first year of the
century or millennium: -100, 1, 101... 1001 2001 etc. Indeed, I don't
think it would make sense to put 2000 (last year of the 2nd millennium)
for rounding all years of the third millenium.

I also fixed the code so that all decades last 10 years and decade 199
means the 1990's.

I have added some tests that are relevant to deal with tricky cases. The
formula may be simplified, but all these cases must pass. Please keep
them.

Have a nice day,

-- 
Fabien Coelho - [EMAIL PROTECTED]
*** ./src/backend/utils/adt/timestamp.c.orig    Fri Jun  4 15:50:58 2004
--- ./src/backend/utils/adt/timestamp.c Tue Aug 10 16:31:41 2004
***************
*** 2727,2737 ****
                                fsec = 0;
                                break;
                        case DTK_MILLENNIUM:
!                               tm->tm_year = (tm->tm_year / 1000) * 1000;
                        case DTK_CENTURY:
!                               tm->tm_year = (tm->tm_year / 100) * 100;
                        case DTK_DECADE:
!                               tm->tm_year = (tm->tm_year / 10) * 10;
                        case DTK_YEAR:
                                tm->tm_mon = 1;
                        case DTK_QUARTER:
--- 2727,2752 ----
                                fsec = 0;
                                break;
                        case DTK_MILLENNIUM:
!                               /* see comments in timestamptz_trunc */
!                               if (tm->tm_year > 0)
!                                       tm->tm_year = ((tm->tm_year+999) / 1000) * 
1000 - 999;
!                               else
!                                       tm->tm_year = - ((999 - (tm->tm_year-1))/1000) 
* 1000 + 1;
                        case DTK_CENTURY:
!                               /* see comments in timestamptz_trunc */
!                               if (tm->tm_year > 0)
!                                       tm->tm_year = ((tm->tm_year+99) / 100) * 100 - 
99;
!                               else
!                                       tm->tm_year = - ((99 - (tm->tm_year-1))/100) * 
100 + 1;
                        case DTK_DECADE:
!                               /* see comments in timestamptz_trunc */
!                               if (val != DTK_MILLENNIUM && val != DTK_CENTURY)
!                               {
!                                       if (tm->tm_year > 0)
!                                               tm->tm_year = (tm->tm_year / 10) * 10;
!                                       else
!                                               tm->tm_year = - ((8-(tm->tm_year-1)) / 
10) * 10;
!                               }
                        case DTK_YEAR:
                                tm->tm_mon = 1;
                        case DTK_QUARTER:
***************
*** 2830,2841 ****
                                tm->tm_sec = 0;
                                fsec = 0;
                                break;
                        case DTK_MILLENNIUM:
!                               tm->tm_year = (tm->tm_year / 1000) * 1000;
                        case DTK_CENTURY:
!                               tm->tm_year = (tm->tm_year / 100) * 100;
                        case DTK_DECADE:
!                               tm->tm_year = (tm->tm_year / 10) * 10;
                        case DTK_YEAR:
                                tm->tm_mon = 1;
                        case DTK_QUARTER:
--- 2845,2877 ----
                                tm->tm_sec = 0;
                                fsec = 0;
                                break;
+                               /* one may consider DTK_THOUSAND and DTK_HUNDRED... */
                        case DTK_MILLENNIUM:
!                               /* truncating to the millennium? what is this supposed 
to mean?
!                                * let us put the first year of the millennium... 
!                                * i.e. -1000, 1, 1001, 2001...
!                                */
!                               if (tm->tm_year > 0)
!                                       tm->tm_year = ((tm->tm_year+999) / 1000) * 
1000 - 999;
!                               else
!                                       tm->tm_year = - ((999 - (tm->tm_year-1))/1000) 
* 1000 + 1;
                        case DTK_CENTURY:
!                               /* truncating to the century? as above: -100, 1, 
101... */
!                               if (tm->tm_year > 0)
!                                       tm->tm_year = ((tm->tm_year+99) / 100) * 100 - 
99 ;
!                               else
!                                       tm->tm_year = - ((99 - (tm->tm_year-1))/100) * 
100 + 1;
                        case DTK_DECADE:
!                               /* truncating to the decade? first year of the decade.
!                                * must not be applied if year was truncated before!
!                                */
!                               if (val != DTK_MILLENNIUM && val != DTK_CENTURY)
!                               {
!                                       if (tm->tm_year > 0)
!                                               tm->tm_year = (tm->tm_year / 10) * 10;
!                                       else
!                                               tm->tm_year = - ((8-(tm->tm_year-1)) / 
10) * 10;
!                               }
                        case DTK_YEAR:
                                tm->tm_mon = 1;
                        case DTK_QUARTER:
***************
*** 2923,2932 ****
--- 2959,2971 ----
                        switch (val)
                        {
                                case DTK_MILLENNIUM:
+                                       /* caution: C division may have negative 
remainder */
                                        tm->tm_year = (tm->tm_year / 1000) * 1000;
                                case DTK_CENTURY:
+                                       /* caution: C division may have negative 
remainder */
                                        tm->tm_year = (tm->tm_year / 100) * 100;
                                case DTK_DECADE:
+                                       /* caution: C division may have negative 
remainder */
                                        tm->tm_year = (tm->tm_year / 10) * 10;
                                case DTK_YEAR:
                                        tm->tm_mon = 0;
***************
*** 3221,3227 ****
                                break;
  
                        case DTK_DECADE:
!                               result = (tm->tm_year / 10);
                                break;
  
                        case DTK_CENTURY:
--- 3260,3273 ----
                                break;
  
                        case DTK_DECADE:
!                               /* what is a decade wrt dates?
!                                * let us assume that decade 199 is 1990 thru 1999...
!                                * decade 0 starts on year 1 BC, and -1 is 11 BC thru 
2 BC...
!                                */
!                               if (tm->tm_year>=0)
!                                       result = (tm->tm_year / 10);
!                               else
!                                       result = -((8-(tm->tm_year-1)) / 10);
                                break;
  
                        case DTK_CENTURY:
***************
*** 3232,3238 ****
                                if (tm->tm_year > 0)
                                        result = ((tm->tm_year+99) / 100);
                                else
!                                       /* caution: C division may yave negative 
remainder */
                                        result = - ((99 - (tm->tm_year-1))/100);
                                break;
  
--- 3278,3284 ----
                                if (tm->tm_year > 0)
                                        result = ((tm->tm_year+99) / 100);
                                else
!                                       /* caution: C division may have negative 
remainder */
                                        result = - ((99 - (tm->tm_year-1))/100);
                                break;
  
***************
*** 3445,3459 ****
                                break;
  
                        case DTK_DECADE:
!                               result = (tm->tm_year / 10);
                                break;
  
                        case DTK_CENTURY:
!                               result = (tm->tm_year / 100);
                                break;
  
                        case DTK_MILLENNIUM:
!                               result = (tm->tm_year / 1000);
                                break;
  
                        case DTK_JULIAN:
--- 3491,3517 ----
                                break;
  
                        case DTK_DECADE:
!                               /* see comments in timestamp_part */
!                               if (tm->tm_year>0)
!                                       result = (tm->tm_year / 10);
!                               else
!                                       result = - ((8-(tm->tm_year-1)) / 10);
                                break;
  
                        case DTK_CENTURY:
!                               /* see comments in timestamp_part */
!                               if (tm->tm_year > 0)
!                                       result = ((tm->tm_year+99) / 100);
!                               else
!                                       result = - ((99 - (tm->tm_year-1))/100);
                                break;
  
                        case DTK_MILLENNIUM:
!                               /* see comments in timestamp_part */
!                               if (tm->tm_year > 0)
!                                       result = ((tm->tm_year+999) / 1000);
!                               else
!                                       result = - ((999 - (tm->tm_year-1))/1000);
                                break;
  
                        case DTK_JULIAN:
***************
*** 3606,3619 ****
--- 3664,3680 ----
                                        break;
  
                                case DTK_DECADE:
+                                       /* caution: C division may have negative 
remainder */
                                        result = (tm->tm_year / 10);
                                        break;
  
                                case DTK_CENTURY:
+                                       /* caution: C division may have negative 
remainder */
                                        result = (tm->tm_year / 100);
                                        break;
  
                                case DTK_MILLENNIUM:
+                                       /* caution: C division may have negative 
remainder */
                                        result = (tm->tm_year / 1000);
                                        break;
  
*** ./src/test/regress/expected/date.out.orig   Mon Apr 12 14:25:37 2004
--- ./src/test/regress/expected/date.out        Tue Aug 10 16:41:12 2004
***************
*** 930,932 ****
--- 930,1081 ----
           3
  (1 row)
  
+ --
+ -- decade
+ --
+ SELECT EXTRACT(DECADE FROM DATE '1994-12-25');    -- 199
+  date_part 
+ -----------
+        199
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0010-01-01');    --   1
+  date_part 
+ -----------
+          1
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0009-12-31');    --   0
+  date_part 
+ -----------
+          0
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0001-01-01 BC'); --   0
+  date_part 
+ -----------
+          0
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0002-12-31 BC'); --  -1
+  date_part 
+ -----------
+         -1
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0011-01-01 BC'); --  -1
+  date_part 
+ -----------
+         -1
+ (1 row)
+ 
+ SELECT EXTRACT(DECADE FROM DATE '0012-12-31 BC'); --  -2
+  date_part 
+ -----------
+         -2
+ (1 row)
+ 
+ --
+ -- some other types:
+ --
+ -- on a timestamp.
+ SELECT EXTRACT(CENTURY FROM NOW())>=21 AS True;       -- true
+  true 
+ ------
+  t
+ (1 row)
+ 
+ SELECT EXTRACT(CENTURY FROM TIMESTAMP '1970-03-20 04:30:00.00000'); -- 20
+  date_part 
+ -----------
+         20
+ (1 row)
+ 
+ -- on an interval
+ SELECT EXTRACT(CENTURY FROM INTERVAL '100 y');  -- 1
+  date_part 
+ -----------
+          1
+ (1 row)
+ 
+ SELECT EXTRACT(CENTURY FROM INTERVAL '99 y');   -- 0
+  date_part 
+ -----------
+          0
+ (1 row)
+ 
+ SELECT EXTRACT(CENTURY FROM INTERVAL '-99 y');  -- 0
+  date_part 
+ -----------
+          0
+ (1 row)
+ 
+ SELECT EXTRACT(CENTURY FROM INTERVAL '-100 y'); -- -1
+  date_part 
+ -----------
+         -1
+ (1 row)
+ 
+ --
+ -- test trunc function!
+ --
+ SELECT DATE_TRUNC('MILLENNIUM', TIMESTAMP '1970-03-20 04:30:00.00000'); -- 1001
+         date_trunc        
+ --------------------------
+  Thu Jan 01 00:00:00 1001
+ (1 row)
+ 
+ SELECT DATE_TRUNC('MILLENNIUM', DATE '1970-03-20'); -- 1001-01-01
+           date_trunc          
+ ------------------------------
+  Thu Jan 01 00:00:00 1001 PST
+ (1 row)
+ 
+ SELECT DATE_TRUNC('CENTURY', TIMESTAMP '1970-03-20 04:30:00.00000'); -- 1901
+         date_trunc        
+ --------------------------
+  Tue Jan 01 00:00:00 1901
+ (1 row)
+ 
+ SELECT DATE_TRUNC('CENTURY', DATE '1970-03-20'); -- 1901
+           date_trunc          
+ ------------------------------
+  Tue Jan 01 00:00:00 1901 PST
+ (1 row)
+ 
+ SELECT DATE_TRUNC('CENTURY', DATE '2004-08-10'); -- 2001-01-01
+           date_trunc          
+ ------------------------------
+  Mon Jan 01 00:00:00 2001 PST
+ (1 row)
+ 
+ SELECT DATE_TRUNC('CENTURY', DATE '0002-02-04'); -- 0001-01-01
+           date_trunc          
+ ------------------------------
+  Mon Jan 01 00:00:00 0001 PST
+ (1 row)
+ 
+ SELECT DATE_TRUNC('CENTURY', DATE '0055-08-10 BC'); -- 0100-01-01 BC
+            date_trunc            
+ ---------------------------------
+  Tue Jan 01 00:00:00 0100 PST BC
+ (1 row)
+ 
+ SELECT DATE_TRUNC('DECADE', DATE '1993-12-25'); -- 1990-01-01
+           date_trunc          
+ ------------------------------
+  Mon Jan 01 00:00:00 1990 PST
+ (1 row)
+ 
+ SELECT DATE_TRUNC('DECADE', DATE '0004-12-25'); -- 0001-01-01 BC
+            date_trunc            
+ ---------------------------------
+  Sat Jan 01 00:00:00 0001 PST BC
+ (1 row)
+ 
+ SELECT DATE_TRUNC('DECADE', DATE '0002-12-31 BC'); -- 0011-01-01 BC
+            date_trunc            
+ ---------------------------------
+  Mon Jan 01 00:00:00 0011 PST BC
+ (1 row)
+ 
*** ./src/test/regress/sql/date.sql.orig        Mon Apr 12 14:25:37 2004
--- ./src/test/regress/sql/date.sql     Tue Aug 10 16:40:13 2004
***************
*** 235,237 ****
--- 235,271 ----
  SELECT EXTRACT(MILLENNIUM FROM DATE '2001-01-01');    --  3
  -- next test to be fixed on the turn of the next millennium;-)
  SELECT EXTRACT(MILLENNIUM FROM CURRENT_DATE);         --  3
+ --
+ -- decade
+ --
+ SELECT EXTRACT(DECADE FROM DATE '1994-12-25');    -- 199
+ SELECT EXTRACT(DECADE FROM DATE '0010-01-01');    --   1
+ SELECT EXTRACT(DECADE FROM DATE '0009-12-31');    --   0
+ SELECT EXTRACT(DECADE FROM DATE '0001-01-01 BC'); --   0
+ SELECT EXTRACT(DECADE FROM DATE '0002-12-31 BC'); --  -1
+ SELECT EXTRACT(DECADE FROM DATE '0011-01-01 BC'); --  -1
+ SELECT EXTRACT(DECADE FROM DATE '0012-12-31 BC'); --  -2
+ --
+ -- some other types:
+ --
+ -- on a timestamp.
+ SELECT EXTRACT(CENTURY FROM NOW())>=21 AS True;       -- true
+ SELECT EXTRACT(CENTURY FROM TIMESTAMP '1970-03-20 04:30:00.00000'); -- 20
+ -- on an interval
+ SELECT EXTRACT(CENTURY FROM INTERVAL '100 y');  -- 1
+ SELECT EXTRACT(CENTURY FROM INTERVAL '99 y');   -- 0
+ SELECT EXTRACT(CENTURY FROM INTERVAL '-99 y');  -- 0
+ SELECT EXTRACT(CENTURY FROM INTERVAL '-100 y'); -- -1
+ --
+ -- test trunc function!
+ --
+ SELECT DATE_TRUNC('MILLENNIUM', TIMESTAMP '1970-03-20 04:30:00.00000'); -- 1001
+ SELECT DATE_TRUNC('MILLENNIUM', DATE '1970-03-20'); -- 1001-01-01
+ SELECT DATE_TRUNC('CENTURY', TIMESTAMP '1970-03-20 04:30:00.00000'); -- 1901
+ SELECT DATE_TRUNC('CENTURY', DATE '1970-03-20'); -- 1901
+ SELECT DATE_TRUNC('CENTURY', DATE '2004-08-10'); -- 2001-01-01
+ SELECT DATE_TRUNC('CENTURY', DATE '0002-02-04'); -- 0001-01-01
+ SELECT DATE_TRUNC('CENTURY', DATE '0055-08-10 BC'); -- 0100-01-01 BC
+ SELECT DATE_TRUNC('DECADE', DATE '1993-12-25'); -- 1990-01-01
+ SELECT DATE_TRUNC('DECADE', DATE '0004-12-25'); -- 0001-01-01 BC
+ SELECT DATE_TRUNC('DECADE', DATE '0002-12-31 BC'); -- 0011-01-01 BC
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