Per a brief conversation with Tom, I've created a patch for adding

support for 'week' within the date_trunc function.

Within the patch I added a couple of test cases and associated target
output, and changed the documentation to add 'week' appropriately.

Robert Creager

doc/src/sgml/func.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.190 2004/03/04 20:09:29 dennis Exp $
+$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.191 2004/03/05 02:41:14 momjian Exp $
 PostgreSQL documentation
 -->
 
@@ -5309,6 +5309,7 @@ date_trunc('<replaceable>field</replaceable>', <replaceable>source</replaceable>
      <member><literal>minute</literal></member>
      <member><literal>hour</literal></member>
      <member><literal>day</literal></member>
+     <member><literal>week</literal></member>
      <member><literal>month</literal></member>
      <member><literal>year</literal></member>
      <member><literal>decade</literal></member>

src/backend/utils/adt/timestamp.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.99 2004/02/14 20:16:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.100 2004/03/05 02:41:14 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2564,6 +2564,13 @@ timestamp_trunc(PG_FUNCTION_ARGS)
 
 		switch (val)
 		{
+			case DTK_WEEK:
+				isoweek2date( date2isoweek( tm->tm_year, tm->tm_mon, tm->tm_mday ), &(tm->tm_year), &(tm->tm_mon), &(tm->tm_mday) );
+				tm->tm_hour = 0;
+				tm->tm_min = 0;
+				tm->tm_sec = 0;
+				fsec = 0;
+				break;
 			case DTK_MILLENNIUM:
 				tm->tm_year = (tm->tm_year / 1000) * 1000;
 			case DTK_CENTURY:
@@ -2672,6 +2679,13 @@ timestamptz_trunc(PG_FUNCTION_ARGS)
 
 		switch (val)
 		{
+			case DTK_WEEK:
+				isoweek2date( date2isoweek( tm->tm_year, tm->tm_mon, tm->tm_mday ), &(tm->tm_year), &(tm->tm_mon), &(tm->tm_mday) );
+				tm->tm_hour = 0;
+				tm->tm_min = 0;
+				tm->tm_sec = 0;
+				fsec = 0;
+				break;
 			case DTK_MILLENNIUM:
 				tm->tm_year = (tm->tm_year / 1000) * 1000;
 			case DTK_CENTURY:

src/test/regress/expected/timestamp.out

@@ -499,6 +499,12 @@ SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
     | @ 1460 days 17 hours 32 mins 1 sec
 (54 rows)
 
+SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc;
+ date_trunc_week |        week_trunc        
+-----------------+--------------------------
+                 | Mon Feb 23 00:00:00 2004
+(1 row)
+
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
   FROM TIMESTAMP_TBL

src/test/regress/expected/timestamptz.out

@@ -494,6 +494,12 @@ SELECT '' AS "54", d1 - timestamp with time zone '1997-01-02' AS diff
     | @ 1460 days 17 hours 32 mins 1 sec
 (54 rows)
 
+SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS week_trunc;
+ date_trunc_week |          week_trunc          
+-----------------+------------------------------
+                 | Mon Feb 23 00:00:00 2004 PST
+(1 row)
+
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp with time zone '1997-01-02' AS diff
   FROM TIMESTAMPTZ_TBL

src/test/regress/sql/timestamp.sql

@@ -151,6 +151,8 @@ SELECT '' AS "49", d1 FROM TIMESTAMP_TBL
 SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
    FROM TIMESTAMP_TBL WHERE d1 BETWEEN '1902-01-01' AND '2038-01-01';
 
+SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp '2004-02-29 15:44:17.71393' ) AS week_trunc;
+
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp without time zone '1997-01-02' AS diff
   FROM TIMESTAMP_TBL

src/test/regress/sql/timestamptz.sql

@@ -145,6 +145,8 @@ SELECT '' AS "49", d1 FROM TIMESTAMPTZ_TBL
 SELECT '' AS "54", d1 - timestamp with time zone '1997-01-02' AS diff
    FROM TIMESTAMPTZ_TBL WHERE d1 BETWEEN '1902-01-01' AND '2038-01-01';
 
+SELECT '' AS date_trunc_week, date_trunc( 'week', timestamp with time zone '2004-02-29 15:44:17.71393' ) AS week_trunc;
+
 -- Test casting within a BETWEEN qualifier
 SELECT '' AS "54", d1 - timestamp with time zone '1997-01-02' AS diff
   FROM TIMESTAMPTZ_TBL