 doc/src/sgml/func.sgml                  |  26 +++++-
 src/backend/utils/adt/timestamp.c       | 151 ++++++++++++++++++++++++++++++++
 src/include/catalog/pg_proc.dat         |   8 ++
 src/test/regress/expected/timestamp.out |  44 ++++++++++
 src/test/regress/sql/timestamp.sql      |  26 ++++++
 5 files changed, 254 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 323366feb6..d518e85411 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -6960,6 +6960,15 @@ SELECT regexp_match('abc01234xyz', '(?:(.*?)(\d+)(.*)){1,1}');
         <entry><literal>2 days 03:00:00</literal></entry>
        </row>
 
+       <row>
+        <entry><literal><function>date_trunc_interval(<type>interval</type>, <type>timestamp</type>)</function></literal></entry>
+        <entry><type>timestamp</type></entry>
+        <entry>Truncate to specified precision; see <xref linkend="functions-datetime-trunc"/>
+        </entry>
+        <entry><literal>date_trunc_interval('15 minutes', timestamp '2001-02-16 20:38:40')</literal></entry>
+        <entry><literal>2001-02-16 20:30:00</literal></entry>
+       </row>
+
        <row>
         <entry>
          <indexterm>
@@ -7829,7 +7838,7 @@ SELECT date_part('hour', INTERVAL '4 hours 3 minutes');
   </sect2>
 
   <sect2 id="functions-datetime-trunc">
-   <title><function>date_trunc</function></title>
+   <title><function>date_trunc</function>, <function>date_trunc_interval</function></title>
 
    <indexterm>
     <primary>date_trunc</primary>
@@ -7913,6 +7922,21 @@ SELECT date_trunc('hour', INTERVAL '3 days 02:47:33');
 <lineannotation>Result: </lineannotation><computeroutput>3 days 02:00:00</computeroutput>
 </screen>
    </para>
+
+   <para>
+    The function <function>date_trunc_interval</function> is 
+    similar to the <function>date_trunc</function>, except that it
+    truncates to an arbitrary interval.
+   </para>
+
+   <para>
+    Example:
+<screen>
+SELECT date_trunc_interval('5 minutes', TIMESTAMP '2001-02-16 20:38:40');
+<lineannotation>Result: </lineannotation><computeroutput>2001-02-16 20:35:00</computeroutput>
+</screen>
+   </para>
+
   </sect2>
 
   <sect2 id="functions-datetime-zoneconvert">
diff --git a/src/backend/utils/adt/timestamp.c b/src/backend/utils/adt/timestamp.c
index 0b6c9d5ea8..2b76ca2c57 100644
--- a/src/backend/utils/adt/timestamp.c
+++ b/src/backend/utils/adt/timestamp.c
@@ -30,6 +30,7 @@
 #include "nodes/nodeFuncs.h"
 #include "nodes/supportnodes.h"
 #include "parser/scansup.h"
+#include "port/pg_bitutils.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
 #include "utils/datetime.h"
@@ -3804,6 +3805,156 @@ timestamptz_age(PG_FUNCTION_ARGS)
  *---------------------------------------------------------*/
 
 
+static Timestamp
+timestamp_trunc_interval_internal(Interval *stride,
+								  Timestamp timestamp,
+								  Timestamp origin)
+{
+	Timestamp	result;
+	fsec_t		ifsec,
+				tfsec;
+	uint32		unit = 0;
+
+	struct pg_tm it;
+	struct pg_tm tt;
+
+	if (interval2tm(*stride, &it, &ifsec) != 0)
+		elog(ERROR, "could not convert interval to tm");
+
+	if (timestamp2tm(timestamp - origin, NULL, &tt, &tfsec, NULL, NULL) != 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+				 errmsg("timestamp out of range")));
+
+	if (it.tm_year != 0)
+	{
+		if (tt.tm_year < 0)
+			tt.tm_year -= tt.tm_year % it.tm_year + it.tm_year;
+		else
+			tt.tm_year -= tt.tm_year % it.tm_year;
+		unit |= DTK_M(DTK_YEAR);
+	}
+	if (it.tm_mon != 0)
+	{
+		tt.tm_mon -= (tt.tm_mon - 1) % it.tm_mon;
+		unit |= DTK_M(DTK_MONTH);
+	}
+	if (it.tm_mday != 0)
+	{
+		tt.tm_mday -= (tt.tm_mday - 1) % it.tm_mday;
+		unit |= DTK_M(DTK_DAY);
+	}
+	if (it.tm_hour != 0)
+	{
+		tt.tm_hour -= tt.tm_hour % it.tm_hour;
+		unit |= DTK_M(DTK_HOUR);
+	}
+	if (it.tm_min != 0)
+	{
+		tt.tm_min -= tt.tm_min % it.tm_min;
+		unit |= DTK_M(DTK_MINUTE);
+	}
+	if (it.tm_sec != 0)
+	{
+		tt.tm_sec -= tt.tm_sec % it.tm_sec;
+		unit |= DTK_M(DTK_SECOND);
+	}
+	if (ifsec != 0)
+	{
+		tfsec -= tfsec % ifsec;
+		unit |= DTK_M(DTK_MICROSEC);
+	}
+
+	/* Justify all smaller timestamp units */
+	switch (unit)
+	{
+		case DTK_M(DTK_YEAR):
+			tt.tm_mon = 1;
+			/* FALL THRU */
+		case DTK_M(DTK_MONTH):
+			tt.tm_mday = 1;
+			/* FALL THRU */
+		case DTK_M(DTK_DAY):
+			tt.tm_hour = 0;
+			/* FALL THRU */
+		case DTK_M(DTK_HOUR):
+			tt.tm_min = 0;
+			/* FALL THRU */
+		case DTK_M(DTK_MINUTE):
+			tt.tm_sec = 0;
+			/* FALL THRU */
+		case DTK_M(DTK_SECOND):
+			tfsec = 0;
+			/* FALL THRU */
+		case DTK_M(DTK_MICROSEC):
+			break;
+		default:
+			if (unit == 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+						 errmsg("interval not initialized")));
+			else
+			{
+				int popcount = pg_popcount32(unit);
+
+				if (popcount > 1)
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+							 errmsg("only one interval unit allowed for truncation")));
+				else
+					ereport(ERROR,
+							(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+							 errmsg("interval unit not supported")));
+			}
+	}
+
+	if (tm2timestamp(&tt, tfsec, NULL, &result) != 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+				 errmsg("timestamp out of range")));
+
+	return result + origin;
+}
+
+/* timestamp_trunc_interval()
+ * Truncate timestamp to specified interval.
+ */
+Datum
+timestamp_trunc_interval(PG_FUNCTION_ARGS)
+{
+	Interval   *stride = PG_GETARG_INTERVAL_P(0);
+	Timestamp	timestamp = PG_GETARG_TIMESTAMP(1);
+	Timestamp	result;
+
+	if (TIMESTAMP_NOT_FINITE(timestamp))
+		PG_RETURN_TIMESTAMP(timestamp);
+
+	result = timestamp_trunc_interval_internal(stride, timestamp, 0);
+
+	PG_RETURN_TIMESTAMP(result);
+}
+
+Datum
+timestamp_trunc_interval_origin(PG_FUNCTION_ARGS)
+{
+	Interval   *stride = PG_GETARG_INTERVAL_P(0);
+	Timestamp	timestamp = PG_GETARG_TIMESTAMP(1);
+	Timestamp	origin = PG_GETARG_TIMESTAMP(2);
+	Timestamp	result;
+
+	if (TIMESTAMP_NOT_FINITE(timestamp))
+		PG_RETURN_TIMESTAMP(timestamp);
+
+	if (TIMESTAMP_NOT_FINITE(origin))
+		ereport(ERROR,
+				(errcode(ERRCODE_DATETIME_VALUE_OUT_OF_RANGE),
+				 errmsg("origin timestamp out of range")));
+
+	result = timestamp_trunc_interval_internal(stride, timestamp, origin);
+
+	PG_RETURN_TIMESTAMP(result);
+}
+
 /* timestamp_trunc()
  * Truncate timestamp to specified units.
  */
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 07a86c7b7b..6216e64862 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5663,6 +5663,14 @@
 { oid => '2020', descr => 'truncate timestamp to specified units',
   proname => 'date_trunc', prorettype => 'timestamp',
   proargtypes => 'text timestamp', prosrc => 'timestamp_trunc' },
+{ oid => '8989', descr => 'truncate timestamp to specified interval',
+  proname => 'date_trunc_interval', prorettype => 'timestamp',
+  proargtypes => 'interval timestamp', prosrc => 'timestamp_trunc_interval' },
+{ oid => '8990',
+  descr => 'truncate timestamp to specified interval and origin',
+  proname => 'date_trunc_interval', prorettype => 'timestamp',
+  proargtypes => 'interval timestamp timestamp',
+  prosrc => 'timestamp_trunc_interval_origin' },
 { oid => '2021', descr => 'extract field from timestamp',
   proname => 'date_part', prorettype => 'float8',
   proargtypes => 'text timestamp', prosrc => 'timestamp_part' },
diff --git a/src/test/regress/expected/timestamp.out b/src/test/regress/expected/timestamp.out
index 5f97505a30..acc6c4b75f 100644
--- a/src/test/regress/expected/timestamp.out
+++ b/src/test/regress/expected/timestamp.out
@@ -545,6 +545,50 @@ SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp '2004-02-29 15:44:17
                  | Mon Feb 23 00:00:00 2004
 (1 row)
 
+-- truncate timestamps on intervals
+SELECT
+  interval,
+  date_trunc_interval(interval::interval, ts)
+FROM (
+  VALUES
+  ('50 years'),
+  ('1 month'),
+  ('2 months'),
+  ('6 months'),
+  ('7 days'),
+  ('15 days'),
+  ('2 hours'),
+  ('15 minutes'),
+  ('10 seconds'),
+  ('100 milliseconds'),
+  ('250 microseconds')
+) intervals (interval),
+(SELECT TIMESTAMP '2020-02-11 15:44:17.71393') ts (ts);
+     interval     |      date_trunc_interval       
+------------------+--------------------------------
+ 50 years         | Sat Jan 01 00:00:00 2000
+ 1 month          | Sat Feb 01 00:00:00 2020
+ 2 months         | Wed Jan 01 00:00:00 2020
+ 6 months         | Wed Jan 01 00:00:00 2020
+ 7 days           | Sat Feb 08 00:00:00 2020
+ 15 days          | Sat Feb 01 00:00:00 2020
+ 2 hours          | Tue Feb 11 14:00:00 2020
+ 15 minutes       | Tue Feb 11 15:30:00 2020
+ 10 seconds       | Tue Feb 11 15:44:10 2020
+ 100 milliseconds | Tue Feb 11 15:44:17.7 2020
+ 250 microseconds | Tue Feb 11 15:44:17.71375 2020
+(11 rows)
+
+-- truncate BC timestamps on intervals
+SELECT date_trunc_interval('100 year'::interval, TIMESTAMP '0055-06-1 01:01:01.0 BC');
+     date_trunc_interval     
+-----------------------------
+ Mon Jan 01 00:00:00 0101 BC
+(1 row)
+
+-- disallow multiple units (ms + us is an exception)
+SELECT date_trunc_interval('1 year 1 microsecond', TIMESTAMP '2001-02-16 20:38:40.123456');
+ERROR:  only one interval unit allowed for truncation
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
   FROM TIMESTAMP_TBL
diff --git a/src/test/regress/sql/timestamp.sql b/src/test/regress/sql/timestamp.sql
index 7b58c3cfa5..9e5d72de84 100644
--- a/src/test/regress/sql/timestamp.sql
+++ b/src/test/regress/sql/timestamp.sql
@@ -166,6 +166,32 @@ SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
 
 SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc;
 
+-- truncate timestamps on intervals
+SELECT
+  interval,
+  date_trunc_interval(interval::interval, ts)
+FROM (
+  VALUES
+  ('50 years'),
+  ('1 month'),
+  ('2 months'),
+  ('6 months'),
+  ('7 days'),
+  ('15 days'),
+  ('2 hours'),
+  ('15 minutes'),
+  ('10 seconds'),
+  ('100 milliseconds'),
+  ('250 microseconds')
+) intervals (interval),
+(SELECT TIMESTAMP '2020-02-11 15:44:17.71393') ts (ts);
+
+-- truncate BC timestamps on intervals
+SELECT date_trunc_interval('100 year'::interval, TIMESTAMP '0055-06-1 01:01:01.0 BC');
+
+-- disallow multiple units (ms + us is an exception)
+SELECT date_trunc_interval('1 year 1 microsecond', TIMESTAMP '2001-02-16 20:38:40.123456');
+
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
   FROM TIMESTAMP_TBL
