Fix AT TIME ZONE (in all three variants) so that we first try to interpret

the timezone argument as a timezone abbreviation, and only try it as a full
timezone name if that fails.  The zic database has four zones (CET, EET, MET,
WET) that are full daylight-savings zones and yet have names that are the
same as their abbreviations for standard time, resulting in ambiguity.
In the timestamp input functions we resolve the ambiguity by preferring the
abbreviation, and AT TIME ZONE should work the same way.  (No functionality
is lost because the zic database also has other names for these zones, eg
Europe/Zurich.)  Per gripe from Jaromir Talir.

Backpatch to 8.1.  Older releases did not have the issue because AT TIME ZONE
only accepted abbreviations not zone names.  (Thus, this patch also arguably
fixes a compatibility botch introduced at 8.1: in ambiguous cases we now
behave the same as 8.0 did.)

src/backend/utils/adt/date.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/date.c,v 1.125.2.1 2007/06/02 16:41:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/date.c,v 1.125.2.2 2008/07/07 18:10:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2508,33 +2508,19 @@ timetz_zone(PG_FUNCTION_ARGS)
 	int			tz;
 	char		tzname[TZ_STRLEN_MAX + 1];
 	int			len;
-	pg_tz	   *tzp;
-
-	/*
-	 * Look up the requested timezone.	First we look in the timezone database
-	 * (to handle cases like "America/New_York"), and if that fails, we look
-	 * in the date token table (to handle cases like "EST").
-	 */
-	len = Min(VARSIZE(zone) - VARHDRSZ, TZ_STRLEN_MAX);
-	memcpy(tzname, VARDATA(zone), len);
-	tzname[len] = '\0';
-	tzp = pg_tzset(tzname);
-	if (tzp)
-	{
-		/* Get the offset-from-GMT that is valid today for the selected zone */
-		pg_time_t	now;
-		struct pg_tm *tm;
-
-		now = time(NULL);
-		tm = pg_localtime(&now, tzp);
-		tz = -tm->tm_gmtoff;
-	}
-	else
-	{
 	char	   *lowzone;
 	int			type,
 				val;
+	pg_tz	   *tzp;
 
+	/*
+	 * Look up the requested timezone.  First we look in the date token table
+	 * (to handle cases like "EST"), and if that fails, we look in the
+	 * timezone database (to handle cases like "America/New_York").  (This
+	 * matches the order in which timestamp input checks the cases; it's
+	 * important because the timezone database unwisely uses a few zone names
+	 * that are identical to offset abbreviations.)
+	 */
 	lowzone = downcase_truncate_identifier(VARDATA(zone),
 										   VARSIZE(zone) - VARHDRSZ,
 										   false);
@@ -2543,6 +2529,22 @@ timetz_zone(PG_FUNCTION_ARGS)
 	if (type == TZ || type == DTZ)
 		tz = val * 60;
 	else
+	{
+		len = Min(VARSIZE(zone) - VARHDRSZ, TZ_STRLEN_MAX);
+		memcpy(tzname, VARDATA(zone), len);
+		tzname[len] = '\0';
+		tzp = pg_tzset(tzname);
+		if (tzp)
+		{
+			/* Get the offset-from-GMT that is valid today for the zone */
+			pg_time_t	now;
+			struct pg_tm *tm;
+
+			now = time(NULL);
+			tm = pg_localtime(&now, tzp);
+			tz = -tm->tm_gmtoff;
+		}
+		else
 		{
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),

src/backend/utils/adt/timestamp.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.169.2.1 2007/09/16 15:56:32 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.169.2.2 2008/07/07 18:10:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -4223,18 +4223,36 @@ timestamp_zone(PG_FUNCTION_ARGS)
 	Timestamp	timestamp = PG_GETARG_TIMESTAMP(1);
 	TimestampTz result;
 	int			tz;
-	pg_tz	   *tzp;
 	char		tzname[TZ_STRLEN_MAX + 1];
 	int			len;
+	char	   *lowzone;
+	int			type,
+				val;
+	pg_tz	   *tzp;
 
 	if (TIMESTAMP_NOT_FINITE(timestamp))
 		PG_RETURN_TIMESTAMPTZ(timestamp);
 
 	/*
-	 * Look up the requested timezone.	First we look in the timezone database
+	 * Look up the requested timezone.  First we look in the date token table
-	 * (to handle cases like "America/New_York"), and if that fails, we look
+	 * (to handle cases like "EST"), and if that fails, we look in the
-	 * in the date token table (to handle cases like "EST").
+	 * timezone database (to handle cases like "America/New_York").  (This
+	 * matches the order in which timestamp input checks the cases; it's
+	 * important because the timezone database unwisely uses a few zone names
+	 * that are identical to offset abbreviations.)
 	 */
+	lowzone = downcase_truncate_identifier(VARDATA(zone),
+										   VARSIZE(zone) - VARHDRSZ,
+										   false);
+	type = DecodeSpecial(0, lowzone, &val);
+
+	if (type == TZ || type == DTZ)
+	{
+		tz = -(val * 60);
+		result = dt2local(timestamp, tz);
+	}
+	else
+	{
 		len = Min(VARSIZE(zone) - VARHDRSZ, TZ_STRLEN_MAX);
 		memcpy(tzname, VARDATA(zone), len);
 		tzname[len] = '\0';
@@ -4257,27 +4275,12 @@ timestamp_zone(PG_FUNCTION_ARGS)
 								tzname)));
 		}
 		else
-	{
-		char	   *lowzone;
-		int			type,
-					val;
-
-		lowzone = downcase_truncate_identifier(VARDATA(zone),
-											   VARSIZE(zone) - VARHDRSZ,
-											   false);
-		type = DecodeSpecial(0, lowzone, &val);
-
-		if (type == TZ || type == DTZ)
-			tz = -(val * 60);
-		else
 		{
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("time zone \"%s\" not recognized", tzname)));
-			tz = 0;				/* keep compiler quiet */
+			result = 0;				/* keep compiler quiet */
 		}
-
-		result = dt2local(timestamp, tz);
 	}
 
 	PG_RETURN_TIMESTAMPTZ(result);
@@ -4396,18 +4399,36 @@ timestamptz_zone(PG_FUNCTION_ARGS)
 	TimestampTz timestamp = PG_GETARG_TIMESTAMPTZ(1);
 	Timestamp	result;
 	int			tz;
-	pg_tz	   *tzp;
 	char		tzname[TZ_STRLEN_MAX + 1];
 	int			len;
+	char	   *lowzone;
+	int			type,
+				val;
+	pg_tz	   *tzp;
 
 	if (TIMESTAMP_NOT_FINITE(timestamp))
 		PG_RETURN_TIMESTAMP(timestamp);
 
 	/*
-	 * Look up the requested timezone.	First we look in the timezone database
+	 * Look up the requested timezone.  First we look in the date token table
-	 * (to handle cases like "America/New_York"), and if that fails, we look
+	 * (to handle cases like "EST"), and if that fails, we look in the
-	 * in the date token table (to handle cases like "EST").
+	 * timezone database (to handle cases like "America/New_York").  (This
+	 * matches the order in which timestamp input checks the cases; it's
+	 * important because the timezone database unwisely uses a few zone names
+	 * that are identical to offset abbreviations.)
 	 */
+	lowzone = downcase_truncate_identifier(VARDATA(zone),
+										   VARSIZE(zone) - VARHDRSZ,
+										   false);
+	type = DecodeSpecial(0, lowzone, &val);
+
+	if (type == TZ || type == DTZ)
+	{
+		tz = val * 60;
+		result = dt2local(timestamp, tz);
+	}
+	else
+	{
 		len = Min(VARSIZE(zone) - VARHDRSZ, TZ_STRLEN_MAX);
 		memcpy(tzname, VARDATA(zone), len);
 		tzname[len] = '\0';
@@ -4429,27 +4450,12 @@ timestamptz_zone(PG_FUNCTION_ARGS)
 								tzname)));
 		}
 		else
-	{
-		char	   *lowzone;
-		int			type,
-					val;
-
-		lowzone = downcase_truncate_identifier(VARDATA(zone),
-											   VARSIZE(zone) - VARHDRSZ,
-											   false);
-		type = DecodeSpecial(0, lowzone, &val);
-
-		if (type == TZ || type == DTZ)
-			tz = val * 60;
-		else
 		{
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("time zone \"%s\" not recognized", tzname)));
-			tz = 0;				/* keep compiler quiet */
+			result = 0;				/* keep compiler quiet */
 		}
-
-		result = dt2local(timestamp, tz);
 	}
 
 	PG_RETURN_TIMESTAMP(result);