Implement SQL92-compatible FIRST, LAST, ABSOLUTE n, RELATIVE n options

for FETCH and MOVE.

doc/src/sgml/ref/move.sgml

 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/move.sgml,v 1.19 2003/03/10 03:53:49 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/move.sgml,v 1.20 2003/03/11 19:40:22 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -21,7 +21,7 @@ PostgreSQL documentation
    <date>1999-07-20</date>
   </refsynopsisdivinfo>
   <synopsis>
-MOVE [ <replaceable class="PARAMETER">direction</replaceable> ] [ <replaceable class="PARAMETER">count</replaceable> ] { IN | FROM } <replaceable class="PARAMETER">cursor</replaceable>
+MOVE [ <replaceable class="PARAMETER">direction</replaceable> { FROM | IN } ] <replaceable class="PARAMETER">cursor</replaceable>
   </synopsis>
  </refsynopsisdiv>
 
@@ -33,9 +33,7 @@ MOVE [ <replaceable class="PARAMETER">direction</replaceable> ] [ <replaceable c
    Description
   </title>
   <para>
-   <command>MOVE</command> allows the user to move the cursor position a 
-   specified number of rows, or to the beginning or end of the cursor.
-   <command>MOVE ALL</command> moves to the end of the cursor.
+   <command>MOVE</command> repositions a cursor without retrieving any data.
    <command>MOVE</command> works exactly like the <command>FETCH</command>
    command, except it only repositions the cursor and does not return rows.
   </para>
@@ -54,8 +52,9 @@ MOVE [ <replaceable class="PARAMETER">direction</replaceable> ] [ <replaceable c
    </title>
 
    <para>
-    <command>MOVE</command> is a <productname>PostgreSQL</productname>
-    language extension.
+    The count returned in <command>MOVE</command>'s status string is the
+    count of the number of rows that would have been returned by the
+    equivalent <command>FETCH</command> command.
    </para>
 
    <para>
@@ -119,9 +118,6 @@ COMMIT WORK;
    </title>
    <para>
     There is no <acronym>SQL92</acronym> <command>MOVE</command> statement. 
-    Instead, <acronym>SQL92</acronym> allows
-    one to <command>FETCH</command> rows from an absolute cursor position,
-    implicitly moving the cursor to the correct position.
    </para>
   </refsect2>
  </refsect1>

src/backend/executor/execMain.c

@@ -26,7 +26,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.201 2003/03/10 03:53:49 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/execMain.c,v 1.202 2003/03/11 19:40:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -287,6 +287,42 @@ ExecutorEnd(QueryDesc *queryDesc)
 	queryDesc->planstate = NULL;
 }
 
+/* ----------------------------------------------------------------
+ *		ExecutorRewind
+ *
+ *		This routine may be called on an open queryDesc to rewind it
+ *		to the start.
+ * ----------------------------------------------------------------
+ */
+void
+ExecutorRewind(QueryDesc *queryDesc)
+{
+	EState	   *estate;
+	MemoryContext oldcontext;
+
+	/* sanity checks */
+	Assert(queryDesc != NULL);
+
+	estate = queryDesc->estate;
+
+	Assert(estate != NULL);
+
+	/* It's probably not sensible to rescan updating queries */
+	Assert(queryDesc->operation == CMD_SELECT);
+
+	/*
+	 * Switch into per-query memory context
+	 */
+	oldcontext = MemoryContextSwitchTo(estate->es_query_cxt);
+
+	/*
+	 * rescan plan
+	 */
+	ExecReScan(queryDesc->planstate, NULL);
+
+	MemoryContextSwitchTo(oldcontext);
+}
+
 
 /*
  * ExecCheckRTPerms

src/backend/executor/spi.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/spi.c,v 1.87 2003/03/10 03:53:49 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/spi.c,v 1.88 2003/03/11 19:40:22 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1349,8 +1349,11 @@ _SPI_cursor_operation(Portal portal, bool forward, int count,
 	_SPI_current->tuptable = NULL;
 
 	/* Run the cursor */
-	_SPI_current->processed = DoPortalFetch(portal, forward, (long) count,
-											dest);
+	_SPI_current->processed =
+		DoPortalFetch(portal,
+					  forward ? FETCH_FORWARD : FETCH_BACKWARD,
+					  (long) count,
+					  dest);
 
 	if (dest == SPI && _SPI_checktuples())
 		elog(FATAL, "SPI_fetch: # of processed tuples check failed");

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.405 2003/03/10 03:53:50 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/gram.y,v 2.406 2003/03/11 19:40:23 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -191,7 +191,7 @@ static void doNegateFloat(Value *v);
 
 %type <range>	qualified_name OptConstrFromTable
 
-%type <str>		opt_id	all_Op MathOp opt_name SpecialRuleRelation
+%type <str>		all_Op MathOp opt_name SpecialRuleRelation
 
 %type <str>		iso_level opt_encoding
 %type <node>	grantee
@@ -248,12 +248,10 @@ static void doNegateFloat(Value *v);
 
 %type <boolean> copy_from
 
-%type <ival>	direction reindex_type drop_type
+%type <ival>	reindex_type drop_type fetch_count
 				opt_column event comment_type cursor_options
 
-%type <ival>	fetch_how_many
-
-%type <node>	select_limit_value select_offset_value
+%type <node>	fetch_direction select_limit_value select_offset_value
 
 %type <list>	OptSeqList
 %type <defelt>	OptSeqElem
@@ -345,7 +343,7 @@ static void doNegateFloat(Value *v);
 	EACH ELSE ENCODING ENCRYPTED END_P ESCAPE EXCEPT
 	EXCLUSIVE EXECUTE EXISTS EXPLAIN EXTERNAL EXTRACT
 
-	FALSE_P FETCH FLOAT_P FOR FORCE FOREIGN FORWARD
+	FALSE_P FETCH FIRST_P FLOAT_P FOR FORCE FOREIGN FORWARD
 	FREEZE FROM FULL FUNCTION
 
 	GLOBAL GRANT GROUP_P
@@ -361,7 +359,7 @@ static void doNegateFloat(Value *v);
 
 	KEY
 
-	LANCOMPILER LANGUAGE LEADING LEFT LEVEL LIKE LIMIT
+	LANCOMPILER LANGUAGE LAST_P LEADING LEFT LEVEL LIKE LIMIT
 	LISTEN LOAD LOCAL LOCALTIME LOCALTIMESTAMP LOCATION
 	LOCK_P
 
@@ -1239,16 +1237,15 @@ opt_drop_behavior:
 		;
 
 
-
 /*****************************************************************************
  *
  *		QUERY :
- *				close <optname>
+ *				close <portalname>
  *
  *****************************************************************************/
 
 ClosePortalStmt:
-			CLOSE opt_id
+			CLOSE name
 				{
 					ClosePortalStmt *n = makeNode(ClosePortalStmt);
 					n->portalname = $2;
@@ -1256,10 +1253,6 @@ ClosePortalStmt:
 				}
 		;
 
-opt_id: 	ColId									{ $$ = $1; }
-			| /*EMPTY*/								{ $$ = NULL; }
-		;
-
 
 /*****************************************************************************
  *
@@ -2583,151 +2576,159 @@ comment_text:
 /*****************************************************************************
  *
  *		QUERY:
- *			fetch/move [forward | backward] [ # | all ] [ in <portalname> ]
- *			fetch [ forward | backward | absolute | relative ]
- *				  [ # | all | next | prior ] [ [ in | from ] <portalname> ]
+ *			fetch/move
  *
  *****************************************************************************/
 
-FetchStmt:	FETCH direction fetch_how_many from_in name
+FetchStmt:	FETCH fetch_direction from_in name
 				{
-					FetchStmt *n = makeNode(FetchStmt);
-					if ($3 < 0)
-					{
-						$3 = -$3;
-						$2 = (($2 == FETCH_FORWARD) ? FETCH_BACKWARD : FETCH_FORWARD);
-					}
-					n->direction = $2;
-					n->howMany = $3;
-					n->portalname = $5;
+					FetchStmt *n = (FetchStmt *) $2;
+					n->portalname = $4;
 					n->ismove = FALSE;
 					$$ = (Node *)n;
 				}
-			| FETCH fetch_how_many from_in name
+			| FETCH name
 				{
 					FetchStmt *n = makeNode(FetchStmt);
-					if ($2 < 0)
-					{
-						n->howMany = -$2;
-						n->direction = FETCH_BACKWARD;
-					}
-					else
-					{
-						n->direction = FETCH_FORWARD;
-						n->howMany = $2;
-					}
-					n->portalname = $4;
+					n->direction = FETCH_FORWARD;
+					n->howMany = 1;
+					n->portalname = $2;
 					n->ismove = FALSE;
 					$$ = (Node *)n;
 				}
-			| FETCH direction from_in name
+			| MOVE fetch_direction from_in name
 				{
-					FetchStmt *n = makeNode(FetchStmt);
-					n->direction = $2;
-					n->howMany = 1;
+					FetchStmt *n = (FetchStmt *) $2;
 					n->portalname = $4;
-					n->ismove = FALSE;
+					n->ismove = TRUE;
 					$$ = (Node *)n;
 				}
-			| FETCH from_in name
+			| MOVE name
 				{
 					FetchStmt *n = makeNode(FetchStmt);
 					n->direction = FETCH_FORWARD;
 					n->howMany = 1;
-					n->portalname = $3;
-					n->ismove = FALSE;
+					n->portalname = $2;
+					n->ismove = TRUE;
 					$$ = (Node *)n;
 				}
-			| FETCH name
+		;
+
+fetch_direction:
+			/*EMPTY*/
 				{
 					FetchStmt *n = makeNode(FetchStmt);
 					n->direction = FETCH_FORWARD;
 					n->howMany = 1;
-					n->portalname = $2;
-					n->ismove = FALSE;
 					$$ = (Node *)n;
 				}
-			| MOVE direction fetch_how_many from_in name
+			| NEXT
 				{
 					FetchStmt *n = makeNode(FetchStmt);
-					if ($3 < 0)
-					{
-						$3 = -$3;
-						$2 = (($2 == FETCH_FORWARD) ? FETCH_BACKWARD : FETCH_FORWARD);
-					}
-					n->direction = $2;
-					n->howMany = $3;
-					n->portalname = $5;
-					n->ismove = TRUE;
+					n->direction = FETCH_FORWARD;
+					n->howMany = 1;
 					$$ = (Node *)n;
 				}
-			| MOVE fetch_how_many from_in name
+			| PRIOR
 				{
 					FetchStmt *n = makeNode(FetchStmt);
-					if ($2 < 0)
-					{
-						n->howMany = -$2;
-						n->direction = FETCH_BACKWARD;
-					}
-					else
-					{
-						n->direction = FETCH_FORWARD;
-						n->howMany = $2;
-					}
-					n->portalname = $4;
-					n->ismove = TRUE;
+					n->direction = FETCH_BACKWARD;
+					n->howMany = 1;
 					$$ = (Node *)n;
 				}
-			| MOVE direction from_in name
+			| FIRST_P
 				{
 					FetchStmt *n = makeNode(FetchStmt);
-					n->direction = $2;
+					n->direction = FETCH_ABSOLUTE;
 					n->howMany = 1;
-					n->portalname = $4;
-					n->ismove = TRUE;
 					$$ = (Node *)n;
 				}
-			| MOVE from_in name
+			| LAST_P
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_ABSOLUTE;
+					n->howMany = -1;
+					$$ = (Node *)n;
+				}
+			| ABSOLUTE fetch_count
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_ABSOLUTE;
+					n->howMany = $2;
+					$$ = (Node *)n;
+				}
+			| RELATIVE fetch_count
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_RELATIVE;
+					n->howMany = $2;
+					$$ = (Node *)n;
+				}
+			| fetch_count
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_FORWARD;
+					n->howMany = $1;
+					$$ = (Node *)n;
+				}
+			| ALL
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_FORWARD;
+					n->howMany = FETCH_ALL;
+					$$ = (Node *)n;
+				}
+			| FORWARD
 				{
 					FetchStmt *n = makeNode(FetchStmt);
 					n->direction = FETCH_FORWARD;
 					n->howMany = 1;
-					n->portalname = $3;
-					n->ismove = TRUE;
 					$$ = (Node *)n;
 				}
-			| MOVE name
+			| FORWARD fetch_count
 				{
 					FetchStmt *n = makeNode(FetchStmt);
 					n->direction = FETCH_FORWARD;
+					n->howMany = $2;
+					$$ = (Node *)n;
+				}
+			| FORWARD ALL
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_FORWARD;
+					n->howMany = FETCH_ALL;
+					$$ = (Node *)n;
+				}
+			| BACKWARD
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_BACKWARD;
 					n->howMany = 1;
-					n->portalname = $2;
-					n->ismove = TRUE;
 					$$ = (Node *)n;
 				}
-		;
-
-direction:	FORWARD									{ $$ = FETCH_FORWARD; }
-			| BACKWARD								{ $$ = FETCH_BACKWARD; }
-			| RELATIVE								{ $$ = FETCH_FORWARD; }
-			| ABSOLUTE
+			| BACKWARD fetch_count
+				{
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_BACKWARD;
+					n->howMany = $2;
+					$$ = (Node *)n;
+				}
+			| BACKWARD ALL
 				{
-					elog(NOTICE,
-					"FETCH / ABSOLUTE not supported, using RELATIVE");
-					$$ = FETCH_FORWARD;
+					FetchStmt *n = makeNode(FetchStmt);
+					n->direction = FETCH_BACKWARD;
+					n->howMany = FETCH_ALL;
+					$$ = (Node *)n;
 				}
 		;
 
-fetch_how_many:
+fetch_count:
 			Iconst									{ $$ = $1; }
 			| '-' Iconst							{ $$ = - $2; }
-			| ALL									{ $$ = INT_MAX; }
-			| NEXT									{ $$ = 1; }
-			| PRIOR									{ $$ = -1; }
 		;
 
-from_in:	IN_P									{}
-			| FROM									{}
+from_in:	FROM									{}
+			| IN_P									{}
 		;
 
 
@@ -7093,6 +7094,7 @@ unreserved_keyword:
 			| EXPLAIN
 			| EXTERNAL
 			| FETCH
+			| FIRST_P
 			| FORCE
 			| FORWARD
 			| FUNCTION
@@ -7115,6 +7117,7 @@ unreserved_keyword:
 			| KEY
 			| LANCOMPILER
 			| LANGUAGE
+			| LAST_P
 			| LEVEL
 			| LISTEN
 			| LOAD
@@ -7170,9 +7173,9 @@ unreserved_keyword:
 			| SCROLL
 			| SECOND_P
 			| SECURITY
-			| SESSION
 			| SEQUENCE
 			| SERIALIZABLE
+			| SESSION
 			| SET
 			| SHARE
 			| SHOW
@@ -7211,8 +7214,8 @@ unreserved_keyword:
 			| VOLATILE
 			| WITH
 			| WITHOUT
-			| WRITE
 			| WORK
+			| WRITE
 			| YEAR_P
 			| ZONE
 		;

src/backend/parser/keywords.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/keywords.c,v 1.134 2003/02/10 04:44:46 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/keywords.c,v 1.135 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -128,6 +128,7 @@ static const ScanKeyword ScanKeywords[] = {
 	{"extract", EXTRACT},
 	{"false", FALSE_P},
 	{"fetch", FETCH},
+	{"first", FIRST_P},
 	{"float", FLOAT_P},
 	{"for", FOR},
 	{"force", FORCE},
@@ -171,6 +172,7 @@ static const ScanKeyword ScanKeywords[] = {
 	{"key", KEY},
 	{"lancompiler", LANCOMPILER},
 	{"language", LANGUAGE},
+	{"last", LAST_P},
 	{"leading", LEADING},
 	{"left", LEFT},
 	{"level", LEVEL},

src/backend/tcop/utility.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.194 2003/03/10 03:53:51 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/tcop/utility.c,v 1.195 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -321,15 +321,8 @@ ProcessUtility(Node *parsetree,
 			break;
 
 		case T_FetchStmt:
-			{
-				FetchStmt  *stmt = (FetchStmt *) parsetree;
-
-				PerformPortalFetch(stmt->portalname,
-								   stmt->direction == FETCH_FORWARD,
-								   stmt->howMany,
-								   (stmt->ismove) ? None : dest,
-								   completionTag);
-			}
+			PerformPortalFetch((FetchStmt *) parsetree, dest,
+							   completionTag);
 			break;
 
 			/*

src/backend/utils/mmgr/portalmem.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/utils/mmgr/portalmem.c,v 1.52 2003/03/10 03:53:51 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/utils/mmgr/portalmem.c,v 1.53 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -167,10 +167,12 @@ PortalSetQuery(Portal portal,
 	AssertArg(PortalIsValid(portal));
 
 	portal->queryDesc = queryDesc;
-	portal->backwardOK = ExecSupportsBackwardScan(queryDesc->plantree);
-	portal->atStart = true;		/* Allow fetch forward only, to start */
-	portal->atEnd = false;
 	portal->cleanup = cleanup;
+	portal->backwardOK = ExecSupportsBackwardScan(queryDesc->plantree);
+	portal->atStart = true;
+	portal->atEnd = false;		/* allow fetches */
+	portal->portalPos = 0;
+	portal->posOverflow = false;
 }
 
 /*
@@ -211,10 +213,12 @@ CreatePortal(const char *name)
 
 	/* initialize portal query */
 	portal->queryDesc = NULL;
-	portal->backwardOK = false;
-	portal->atStart = true;		/* disallow fetches until query is set */
-	portal->atEnd = true;
 	portal->cleanup = NULL;
+	portal->backwardOK = false;
+	portal->atStart = true;
+	portal->atEnd = true;		/* disallow fetches until query is set */
+	portal->portalPos = 0;
+	portal->posOverflow = false;
 
 	/* put portal in table */
 	PortalHashTableInsert(portal);

src/include/commands/portalcmds.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: portalcmds.h,v 1.5 2003/03/10 03:53:51 tgl Exp $
+ * $Id: portalcmds.h,v 1.6 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,10 +19,12 @@
 
 extern void PerformCursorOpen(DeclareCursorStmt *stmt, CommandDest dest);
 
-extern void PerformPortalFetch(char *name, bool forward, long count,
-				   CommandDest dest, char *completionTag);
+extern void PerformPortalFetch(FetchStmt *stmt, CommandDest dest,
+							   char *completionTag);
 
-extern long DoPortalFetch(Portal portal, bool forward, long count,
+extern long DoPortalFetch(Portal portal,
+						  FetchDirection fdirection,
+						  long count,
 						  CommandDest dest);
 
 extern void PerformPortalClose(char *name);

src/include/executor/executor.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: executor.h,v 1.90 2003/03/10 03:53:51 tgl Exp $
+ * $Id: executor.h,v 1.91 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -86,6 +86,7 @@ extern void ExecutorStart(QueryDesc *queryDesc);
 extern TupleTableSlot *ExecutorRun(QueryDesc *queryDesc,
 			ScanDirection direction, long count);
 extern void ExecutorEnd(QueryDesc *queryDesc);
+extern void ExecutorRewind(QueryDesc *queryDesc);
 extern void ExecCheckRTPerms(List *rangeTable, CmdType operation);
 extern void ExecEndPlan(PlanState *planstate, EState *estate);
 extern void ExecConstraints(const char *caller, ResultRelInfo *resultRelInfo,

src/include/nodes/parsenodes.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: parsenodes.h,v 1.232 2003/03/10 03:53:51 tgl Exp $
+ * $Id: parsenodes.h,v 1.233 2003/03/11 19:40:23 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1228,16 +1228,21 @@ typedef struct ClosePortalStmt
  */
 typedef enum FetchDirection
 {
+	/* for these, howMany is how many rows to fetch; FETCH_ALL means ALL */
 	FETCH_FORWARD,
-	FETCH_BACKWARD
-	/* ABSOLUTE someday? */
+	FETCH_BACKWARD,
+	/* for these, howMany indicates a position; only one row is fetched */
+	FETCH_ABSOLUTE,
+	FETCH_RELATIVE
 } FetchDirection;
 
+#define FETCH_ALL	LONG_MAX
+
 typedef struct FetchStmt
 {
 	NodeTag		type;
 	FetchDirection direction;	/* see above */
-	long		howMany;		/* number of rows */
+	long		howMany;		/* number of rows, or position argument */
 	char	   *portalname;		/* name of portal (cursor) */
 	bool		ismove;			/* TRUE if MOVE */
 } FetchStmt;

src/include/utils/portal.h

@@ -9,7 +9,7 @@
  * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: portal.h,v 1.38 2003/03/10 03:53:52 tgl Exp $
+ * $Id: portal.h,v 1.39 2003/03/11 19:40:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -27,10 +27,21 @@ typedef struct PortalData
 	char	   *name;			/* Portal's name */
 	MemoryContext heap;			/* subsidiary memory */
 	QueryDesc  *queryDesc;		/* Info about query associated with portal */
-	bool		backwardOK;		/* is fetch backwards allowed at all? */
-	bool		atStart;		/* T => fetch backwards is not allowed now */
-	bool		atEnd;			/* T => fetch forwards is not allowed now */
 	void		(*cleanup) (Portal);	/* Cleanup routine (optional) */
+	bool		backwardOK;		/* is fetch backwards allowed? */
+	/*
+	 * atStart, atEnd and portalPos indicate the current cursor position.
+	 * portalPos is zero before the first row, N after fetching N'th row of
+	 * query.  After we run off the end, portalPos = # of rows in query, and
+	 * atEnd is true.  If portalPos overflows, set posOverflow (this causes
+	 * us to stop relying on its value for navigation).  Note that atStart
+	 * implies portalPos == 0, but not the reverse (portalPos could have
+	 * overflowed).
+	 */
+	bool		atStart;
+	bool		atEnd;
+	bool		posOverflow;
+	long		portalPos;
 } PortalData;
 
 /*