timestamptz_trunc() should only recalculate the timezone when truncating

to DAY precision or coarser; leave the timezone alone when precision is
HOUR or less.  This avoids surprises for inputs near a DST transition
time, as per example from Matthew Gabeler-Lee.  (The only reason we
recalculate at all is so that outputs that are supposed to represent
days will come out as local midnight, and that's not relevant for sub-day
precision.)

diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 83286502e81dfaac98296a48a25a0b64a9f4d2ec..0b7190c345582ec7f4a4d3ad46872257676212cc 100644 (file)
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.113 2004/08/30 02:54:39 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.114 2004/11/01 22:00:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2842,6 +2842,7 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
    int         tz;
    int         type,
                val;
+   bool        redotz = false;
    char       *lowunits;
    fsec_t      fsec;
    char       *tzn;
@@ -2872,6 +2873,7 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
                tm->tm_min = 0;
                tm->tm_sec = 0;
                fsec = 0;
+               redotz = true;
                break;
                /* one may consider DTK_THOUSAND and DTK_HUNDRED... */
            case DTK_MILLENNIUM:
@@ -2885,12 +2887,14 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
                    tm->tm_year = ((tm->tm_year + 999) / 1000) * 1000 - 999;
                else
                    tm->tm_year = -((999 - (tm->tm_year - 1)) / 1000) * 1000 + 1;
+               /* FALL THRU */
            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;
+               /* FALL THRU */
            case DTK_DECADE:
 
                /*
@@ -2904,18 +2908,26 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
                    else
                        tm->tm_year = -((8 - (tm->tm_year - 1)) / 10) * 10;
                }
+               /* FALL THRU */
            case DTK_YEAR:
                tm->tm_mon = 1;
+               /* FALL THRU */
            case DTK_QUARTER:
                tm->tm_mon = (3 * ((tm->tm_mon - 1) / 3)) + 1;
+               /* FALL THRU */
            case DTK_MONTH:
                tm->tm_mday = 1;
+               /* FALL THRU */
            case DTK_DAY:
                tm->tm_hour = 0;
+               redotz = true;  /* for all cases >= DAY */
+               /* FALL THRU */
            case DTK_HOUR:
                tm->tm_min = 0;
+               /* FALL THRU */
            case DTK_MINUTE:
                tm->tm_sec = 0;
+               /* FALL THRU */
            case DTK_SECOND:
                fsec = 0;
                break;
@@ -2941,7 +2953,8 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
                result = 0;
        }
 
-       tz = DetermineLocalTimeZone(tm);
+       if (redotz)
+           tz = DetermineLocalTimeZone(tm);
 
        if (tm2timestamp(tm, fsec, &tz, &result) != 0)
            ereport(ERROR,