From: Massimo Dal Zotto <dz@cs.unitn.it>

> sequence.patch
>
>       adds the missing setval command to sequences. Owner of sequences
>       can now set the last value to any value between min and max
>       without recreating the sequence. This is useful after loading
>       data from external files.

Author: scrappy

src/backend/commands/sequence.c

@@ -9,6 +9,7 @@
 #include <string.h>
 
 #include <postgres.h>
+#include <miscadmin.h>
 
 #include <storage/bufmgr.h>
 #include <storage/bufpage.h>
@@ -18,6 +19,7 @@
 #include <commands/creatinh.h>
 #include <commands/sequence.h>
 #include <utils/builtins.h>
+#include <utils/acl.h>
 
 #define SEQ_MAGIC	  0x1717
 
@@ -311,6 +313,52 @@ currval(struct varlena * seqin)
 
 }
 
+int4
+setval(struct varlena * seqin, int4 next)
+{
+	char	*seqname = textout(seqin);
+	SeqTable	elm;
+	Buffer	buf;
+	SequenceTupleForm seq;
+	ItemPointerData iptr;
+
+#ifndef NO_SECURITY
+	if (pg_aclcheck(seqname, getpgusername(), ACL_WR) != ACLCHECK_OK)
+		elog(ERROR, "%s.setval: you don't have permissions to set sequence %s",
+			 seqname, seqname);
+#endif
+
+	/* open and WIntentLock sequence */
+	elm = init_sequence ("setval", seqname);
+	seq = read_info ("setval", elm, &buf);	/* lock page and read tuple */
+
+	if ( seq->cache_value != 1 ) {
+		elog (ERROR, "%s.setval: can't set value of sequence %s, cache != 1",
+			  seqname, seqname);
+	}
+
+	if ((next < seq->min_value) || (next > seq->max_value)) {
+		elog (ERROR, "%s.setval: value %d is of of bounds (%d,%d)",
+			  seqname, next, seq->min_value, seq->max_value);
+	}
+
+	/* save info in local cache */
+	elm->last = next;			/* last returned number */
+	elm->cached = next;			/* last cached number */
+
+	/* save info in sequence relation */
+	seq->last_value = next;		/* last fetched number */
+	seq->is_called = 't';
+
+	if ( WriteBuffer (buf) == STATUS_ERROR )
+		elog (ERROR, "%s.settval: WriteBuffer failed", seqname);
+
+	ItemPointerSet(&iptr, 0, FirstOffsetNumber);
+	RelationUnsetSingleWLockPage (elm->rel, &iptr);
+
+	return (next);
+}
+
 static SequenceTupleForm
 read_info(char *caller, SeqTable elm, Buffer *buf)
 {

src/backend/parser/parse_func.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_func.c,v 1.25 1998/08/19 02:02:20 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_func.c,v 1.26 1998/08/25 21:25:42 scrappy Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -427,15 +427,16 @@ ParseFuncOrColumn(ParseState *pstate, char *funcname, List *fargs,
 	 * Sequence handling.
 	 */
 	if (funcid == F_NEXTVAL ||
-		funcid == F_CURRVAL)
+		funcid == F_CURRVAL ||
+		funcid == F_SETVAL)
 	{
 		Const	   *seq;
 		char	   *seqrel;
 		text	   *seqname;
 		int32		aclcheck_result = -1;
 		extern text *lower(text *string);
 
-		Assert(length(fargs) == 1);
+		Assert(length(fargs) == ((funcid == F_SETVAL) ? 2 : 1));
 		seq = (Const *) lfirst(fargs);
 		if (!IsA((Node *) seq, Const))
 			elog(ERROR, "Only constant sequence names are acceptable for function '%s'", funcname);
@@ -445,7 +446,8 @@ ParseFuncOrColumn(ParseState *pstate, char *funcname, List *fargs,
 		seqrel = textout(seqname);
 
 		if ((aclcheck_result = pg_aclcheck(seqrel, GetPgUserName(),
-			   ((funcid == F_NEXTVAL) ? ACL_WR : ACL_RD)))
+			   (((funcid == F_NEXTVAL) || (funcid == F_SETVAL)) ? 
+				ACL_WR : ACL_RD)))
 			!= ACLCHECK_OK)
 			elog(ERROR, "%s.%s: %s",
 			  seqrel, funcname, aclcheck_error_strings[aclcheck_result]);
@@ -454,6 +456,8 @@ ParseFuncOrColumn(ParseState *pstate, char *funcname, List *fargs,
 
 		if (funcid == F_NEXTVAL && pstate->p_in_where_clause)
 			elog(ERROR, "Sequence function nextval is not allowed in WHERE clauses");
+		if (funcid == F_SETVAL && pstate->p_in_where_clause)
+			elog(ERROR, "Sequence function setval is not allowed in WHERE clauses");
 	}
 
 	expr = makeNode(Expr);

src/include/catalog/pg_proc.h

@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: pg_proc.h,v 1.67 1998/08/24 01:38:08 momjian Exp $
+ * $Id: pg_proc.h,v 1.68 1998/08/25 21:25:44 scrappy Exp $
  *
  * NOTES
  *	  The script catalog/genbki.sh reads this file and generates .bki
@@ -2029,6 +2029,8 @@ DATA(insert OID =  1317 (  nextval	   PGUID 11 f t f 1 f 23 "25" 100 0 0 100  fo
 DESCR("sequence next value");
 DATA(insert OID =  1319 (  currval	   PGUID 11 f t f 1 f 23 "25" 100 0 0 100  foo bar ));
 DESCR("sequence current value");
+DATA(insert OID =  1618 (  setval	   PGUID 11 f t f 2 f 23 "25 23" 100 0 0 100  foo bar ));
+DESCR("sequence set value");
 
 /* for multi-byte support */
 DATA(insert OID = 1039 (  getdatabaseencoding	   PGUID 11 f t f 0 f 19 "0" 100 0 0 100  foo bar ));

src/include/commands/sequence.h

@@ -30,6 +30,7 @@
 extern void DefineSequence(CreateSeqStmt *stmt);
 extern int4 nextval(struct varlena * seqname);
 extern int4 currval(struct varlena * seqname);
+extern int4 setval (struct varlena * seqname, int4 next);
 extern void CloseSequences(void);
 
 #endif							/* SEQUENCE_H */