Change return type of EXTRACT to numeric

The previous implementation of EXTRACT mapped internally to
date_part(), which returned type double precision (since it was
implemented long before the numeric type existed).  This can lead to
imprecise output in some cases, so returning numeric would be
preferrable.  Changing the return type of an existing function is a
bit risky, so instead we do the following:  We implement a new set of
functions, which are now called "extract", in parallel to the existing
date_part functions.  They work the same way internally but use
numeric instead of float8.  The EXTRACT construct is now mapped by the
parser to these new extract functions.  That way, dumps of views
etc. from old versions (which would use date_part) continue to work
unchanged, but new uses will map to the new extract functions.

Additionally, the reverse compilation of EXTRACT now reproduces the
original syntax, using the new mechanism introduced in
40c24bfef92530bd846e111c1742c2a54441c62c.

The following minor changes of behavior result from the new
implementation:

- The column name from an isolated EXTRACT call is now "extract"
  instead of "date_part".

- Extract from date now rejects inappropriate field names such as
  HOUR.  It was previously mapped internally to extract from
  timestamp, so it would silently accept everything appropriate for
  timestamp.

- Return values when extracting fields with possibly fractional
  values, such as second and epoch, now have the full scale that the
  value has internally (so, for example, '1.000000' instead of just
  '1').

Reported-by: Petr Fedorov <petr.fedorov@phystech.edu>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/42b73d2d-da12-ba9f-570a-420e0cce19d9@phystech.edu

1 files changed, 275 insertions, 33 deletions

diff --git a/src/backend/utils/adt/date.c b/src/backend/utils/adt/date.c
index 6053d0e8a6f..83036e5985e 100644
--- a/src/backend/utils/adt/date.c
+++ b/src/backend/utils/adt/date.c
@@ -31,6 +31,7 @@
 #include "utils/builtins.h"
 #include "utils/date.h"
 #include "utils/datetime.h"
+#include "utils/numeric.h"
 #include "utils/sortsupport.h"
 
 /*
@@ -1063,6 +1064,182 @@ in_range_date_interval(PG_FUNCTION_ARGS)
 }
 
 
+/* extract_date()
+ * Extract specified field from date type.
+ */
+Datum
+extract_date(PG_FUNCTION_ARGS)
+{
+	text	   *units = PG_GETARG_TEXT_PP(0);
+	DateADT		date = PG_GETARG_DATEADT(1);
+	int64		intresult;
+	int			type,
+				val;
+	char	   *lowunits;
+	int			year,
+				mon,
+				mday;
+
+	lowunits = downcase_truncate_identifier(VARDATA_ANY(units),
+											VARSIZE_ANY_EXHDR(units),
+											false);
+
+	type = DecodeUnits(0, lowunits, &val);
+	if (type == UNKNOWN_FIELD)
+		type = DecodeSpecial(0, lowunits, &val);
+
+	if (DATE_NOT_FINITE(date) && (type == UNITS || type == RESERV))
+	{
+		switch (val)
+		{
+				/* Oscillating units */
+			case DTK_DAY:
+			case DTK_MONTH:
+			case DTK_QUARTER:
+			case DTK_WEEK:
+			case DTK_DOW:
+			case DTK_ISODOW:
+			case DTK_DOY:
+				PG_RETURN_NULL();
+				break;
+
+				/* Monotonically-increasing units */
+			case DTK_YEAR:
+			case DTK_DECADE:
+			case DTK_CENTURY:
+			case DTK_MILLENNIUM:
+			case DTK_JULIAN:
+			case DTK_ISOYEAR:
+			case DTK_EPOCH:
+				if (DATE_IS_NOBEGIN(date))
+					PG_RETURN_NUMERIC(DatumGetNumeric(DirectFunctionCall3(numeric_in,
+																		  CStringGetDatum("-Infinity"),
+																		  ObjectIdGetDatum(InvalidOid),
+																		  Int32GetDatum(-1))));
+				else
+					PG_RETURN_NUMERIC(DatumGetNumeric(DirectFunctionCall3(numeric_in,
+																		  CStringGetDatum("Infinity"),
+																		  ObjectIdGetDatum(InvalidOid),
+																		  Int32GetDatum(-1))));
+			default:
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("date units \"%s\" not supported",
+								lowunits)));
+		}
+	}
+	else if (type == UNITS)
+	{
+		j2date(date + POSTGRES_EPOCH_JDATE, &year, &mon, &mday);
+
+		switch (val)
+		{
+			case DTK_DAY:
+				intresult = mday;
+				break;
+
+			case DTK_MONTH:
+				intresult = mon;
+				break;
+
+			case DTK_QUARTER:
+				intresult = (mon - 1) / 3 + 1;
+				break;
+
+			case DTK_WEEK:
+				intresult = date2isoweek(year, mon, mday);
+				break;
+
+			case DTK_YEAR:
+				if (year > 0)
+					intresult = year;
+				else
+					/* there is no year 0, just 1 BC and 1 AD */
+					intresult = year - 1;
+				break;
+
+			case DTK_DECADE:
+				/* see comments in timestamp_part */
+				if (year >= 0)
+					intresult = year / 10;
+				else
+					intresult = -((8 - (year - 1)) / 10);
+				break;
+
+			case DTK_CENTURY:
+				/* see comments in timestamp_part */
+				if (year > 0)
+					intresult = (year + 99) / 100;
+				else
+					intresult = -((99 - (year - 1)) / 100);
+				break;
+
+			case DTK_MILLENNIUM:
+				/* see comments in timestamp_part */
+				if (year > 0)
+					intresult = (year + 999) / 1000;
+				else
+					intresult = -((999 - (year - 1)) / 1000);
+				break;
+
+			case DTK_JULIAN:
+				intresult = date + POSTGRES_EPOCH_JDATE;
+				break;
+
+			case DTK_ISOYEAR:
+				intresult = date2isoyear(year, mon, mday);
+				/* Adjust BC years */
+				if (intresult <= 0)
+					intresult -= 1;
+				break;
+
+			case DTK_DOW:
+			case DTK_ISODOW:
+				intresult = j2day(date + POSTGRES_EPOCH_JDATE);
+				if (val == DTK_ISODOW && intresult == 0)
+					intresult = 7;
+				break;
+
+			case DTK_DOY:
+				intresult = date2j(year, mon, mday) - date2j(year, 1, 1) + 1;
+				break;
+
+			default:
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("date units \"%s\" not supported",
+								lowunits)));
+				intresult = 0;
+		}
+	}
+	else if (type == RESERV)
+	{
+		switch (val)
+		{
+			case DTK_EPOCH:
+				intresult = ((int64) date + POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY;
+				break;
+
+			default:
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+						 errmsg("date units \"%s\" not supported",
+								lowunits)));
+				intresult = 0;
+		}
+	}
+	else
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("date units \"%s\" not recognized", lowunits)));
+		intresult = 0;
+	}
+
+	PG_RETURN_NUMERIC(int64_to_numeric(intresult));
+}
+
+
 /* Add an interval to a date, giving a new date.
  * Must handle both positive and negative intervals.
  *
@@ -1949,15 +2126,15 @@ in_range_time_interval(PG_FUNCTION_ARGS)
 }
 
 
-/* time_part()
+/* time_part() and extract_time()
  * Extract specified field from time type.
  */
-Datum
-time_part(PG_FUNCTION_ARGS)
+static Datum
+time_part_common(PG_FUNCTION_ARGS, bool retnumeric)
 {
 	text	   *units = PG_GETARG_TEXT_PP(0);
 	TimeADT		time = PG_GETARG_TIMEADT(1);
-	float8		result;
+	int64		intresult;
 	int			type,
 				val;
 	char	   *lowunits;
@@ -1981,23 +2158,37 @@ time_part(PG_FUNCTION_ARGS)
 		switch (val)
 		{
 			case DTK_MICROSEC:
-				result = tm->tm_sec * 1000000.0 + fsec;
+				intresult = tm->tm_sec * 1000000 + fsec;
 				break;
 
 			case DTK_MILLISEC:
-				result = tm->tm_sec * 1000.0 + fsec / 1000.0;
+				if (retnumeric)
+					/*---
+					 * tm->tm_sec * 1000 + fsec / 1000
+					 * = (tm->tm_sec * 1'000'000 + fsec) / 1000
+					 */
+					PG_RETURN_NUMERIC(int64_div_fast_to_numeric(tm->tm_sec * 1000000LL + fsec, 3));
+				else
+					PG_RETURN_FLOAT8(tm->tm_sec * 1000.0 + fsec / 1000.0);
 				break;
 
 			case DTK_SECOND:
-				result = tm->tm_sec + fsec / 1000000.0;
+				if (retnumeric)
+					/*---
+					 * tm->tm_sec + fsec / 1'000'000
+					 * = (tm->tm_sec * 1'000'000 + fsec) / 1'000'000
+					 */
+					PG_RETURN_NUMERIC(int64_div_fast_to_numeric(tm->tm_sec * 1000000LL + fsec, 6));
+				else
+					PG_RETURN_FLOAT8(tm->tm_sec + fsec / 1000000.0);
 				break;
 
 			case DTK_MINUTE:
-				result = tm->tm_min;
+				intresult = tm->tm_min;
 				break;
 
 			case DTK_HOUR:
-				result = tm->tm_hour;
+				intresult = tm->tm_hour;
 				break;
 
 			case DTK_TZ:
@@ -2016,12 +2207,15 @@ time_part(PG_FUNCTION_ARGS)
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 						 errmsg("\"time\" units \"%s\" not recognized",
 								lowunits)));
-				result = 0;
+				intresult = 0;
 		}
 	}
 	else if (type == RESERV && val == DTK_EPOCH)
 	{
-		result = time / 1000000.0;
+		if (retnumeric)
+			PG_RETURN_NUMERIC(int64_div_fast_to_numeric(time, 6));
+		else
+			PG_RETURN_FLOAT8(time / 1000000.0);
 	}
 	else
 	{
@@ -2029,10 +2223,25 @@ time_part(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("\"time\" units \"%s\" not recognized",
 						lowunits)));
-		result = 0;
+		intresult = 0;
 	}
 
-	PG_RETURN_FLOAT8(result);
+	if (retnumeric)
+		PG_RETURN_NUMERIC(int64_to_numeric(intresult));
+	else
+		PG_RETURN_FLOAT8(intresult);
+}
+
+Datum
+time_part(PG_FUNCTION_ARGS)
+{
+	return time_part_common(fcinfo, false);
+}
+
+Datum
+extract_time(PG_FUNCTION_ARGS)
+{
+	return time_part_common(fcinfo, true);
 }
 
 
@@ -2686,15 +2895,15 @@ datetimetz_timestamptz(PG_FUNCTION_ARGS)
 }
 
 
-/* timetz_part()
+/* timetz_part() and extract_timetz()
  * Extract specified field from time type.
  */
-Datum
-timetz_part(PG_FUNCTION_ARGS)
+static Datum
+timetz_part_common(PG_FUNCTION_ARGS, bool retnumeric)
 {
 	text	   *units = PG_GETARG_TEXT_PP(0);
 	TimeTzADT  *time = PG_GETARG_TIMETZADT_P(1);
-	float8		result;
+	int64		intresult;
 	int			type,
 				val;
 	char	   *lowunits;
@@ -2709,7 +2918,6 @@ timetz_part(PG_FUNCTION_ARGS)
 
 	if (type == UNITS)
 	{
-		double		dummy;
 		int			tz;
 		fsec_t		fsec;
 		struct pg_tm tt,
@@ -2720,38 +2928,49 @@ timetz_part(PG_FUNCTION_ARGS)
 		switch (val)
 		{
 			case DTK_TZ:
-				result = -tz;
+				intresult = -tz;
 				break;
 
 			case DTK_TZ_MINUTE:
-				result = -tz;
-				result /= SECS_PER_MINUTE;
-				FMODULO(result, dummy, (double) MINS_PER_HOUR);
+				intresult = (-tz / SECS_PER_MINUTE) % MINS_PER_HOUR;
 				break;
 
 			case DTK_TZ_HOUR:
-				dummy = -tz;
-				FMODULO(dummy, result, (double) SECS_PER_HOUR);
+				intresult = -tz / SECS_PER_HOUR;
 				break;
 
 			case DTK_MICROSEC:
-				result = tm->tm_sec * 1000000.0 + fsec;
+				intresult = tm->tm_sec * 1000000 + fsec;
 				break;
 
 			case DTK_MILLISEC:
-				result = tm->tm_sec * 1000.0 + fsec / 1000.0;
+				if (retnumeric)
+					/*---
+					 * tm->tm_sec * 1000 + fsec / 1000
+					 * = (tm->tm_sec * 1'000'000 + fsec) / 1000
+					 */
+					PG_RETURN_NUMERIC(int64_div_fast_to_numeric(tm->tm_sec * 1000000LL + fsec, 3));
+				else
+					PG_RETURN_FLOAT8(tm->tm_sec * 1000.0 + fsec / 1000.0);
 				break;
 
 			case DTK_SECOND:
-				result = tm->tm_sec + fsec / 1000000.0;
+				if (retnumeric)
+					/*---
+					 * tm->tm_sec + fsec / 1'000'000
+					 * = (tm->tm_sec * 1'000'000 + fsec) / 1'000'000
+					 */
+					PG_RETURN_NUMERIC(int64_div_fast_to_numeric(tm->tm_sec * 1000000LL + fsec, 6));
+				else
+					PG_RETURN_FLOAT8(tm->tm_sec + fsec / 1000000.0);
 				break;
 
 			case DTK_MINUTE:
-				result = tm->tm_min;
+				intresult = tm->tm_min;
 				break;
 
 			case DTK_HOUR:
-				result = tm->tm_hour;
+				intresult = tm->tm_hour;
 				break;
 
 			case DTK_DAY:
@@ -2766,12 +2985,19 @@ timetz_part(PG_FUNCTION_ARGS)
 						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 						 errmsg("\"time with time zone\" units \"%s\" not recognized",
 								lowunits)));
-				result = 0;
+				intresult = 0;
 		}
 	}
 	else if (type == RESERV && val == DTK_EPOCH)
 	{
-		result = time->time / 1000000.0 + time->zone;
+		if (retnumeric)
+			/*---
+			 * time->time / 1'000'000 + time->zone
+			 * = (time->time + time->zone * 1'000'000) / 1'000'000
+			 */
+			PG_RETURN_NUMERIC(int64_div_fast_to_numeric(time->time + time->zone * 1000000LL, 6));
+		else
+			PG_RETURN_FLOAT8(time->time / 1000000.0 + time->zone);
 	}
 	else
 	{
@@ -2779,10 +3005,26 @@ timetz_part(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("\"time with time zone\" units \"%s\" not recognized",
 						lowunits)));
-		result = 0;
+		intresult = 0;
 	}
 
-	PG_RETURN_FLOAT8(result);
+	if (retnumeric)
+		PG_RETURN_NUMERIC(int64_to_numeric(intresult));
+	else
+		PG_RETURN_FLOAT8(intresult);
+}
+
+
+Datum
+timetz_part(PG_FUNCTION_ARGS)
+{
+	return timetz_part_common(fcinfo, false);
+}
+
+Datum
+extract_timetz(PG_FUNCTION_ARGS)
+{
+	return timetz_part_common(fcinfo, true);
 }
 
 /* timetz_zone()