Add a function lastval(), which returns the value returned by the

last nextval() or setval() performed by the current session. Update the
docs, add regression tests, and bump the catalog version. Patch from
Dennis Björklund, various improvements by Neil Conway.

Author: Neil Conway

doc/src/sgml/func.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.251 2005/06/06 16:29:01 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.252 2005/06/07 07:08:34 neilc Exp $
 PostgreSQL documentation
 -->
 
@@ -6487,6 +6487,9 @@ SELECT TIMESTAMP 'now';  -- incorrect for use with DEFAULT
   <indexterm>
    <primary>currval</primary>
   </indexterm>
+  <indexterm>
+   <primary>lastval</primary>
+  </indexterm>
   <indexterm>
    <primary>setval</primary>
   </indexterm>
@@ -6519,6 +6522,12 @@ SELECT TIMESTAMP 'now';  -- incorrect for use with DEFAULT
       <row>
         <entry><literal><function>currval</function>(<type>text</type>)</literal></entry>
         <entry><type>bigint</type></entry>
+        <entry>Return value most recently obtained with
+        <function>nextval</function> for specified sequence</entry>
+      </row>
+      <row>
+        <entry><literal><function>lastval</function>()</literal></entry>
+        <entry><type>bigint</type></entry>
         <entry>Return value most recently obtained with <function>nextval</function></entry>
       </row>
       <row>
@@ -6587,6 +6596,22 @@ nextval('foo')              <lineannotation>searches search path for <literal>fo
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><function>lastval</function></term>
+      <listitem>
+       <para>
+        Return the value most recently returned by
+        <function>nextval</> in the current session. This function is
+        identical to <function>currval</function>, except that instead
+        of taking the sequence name as an argument it fetches the
+        value of the last sequence that <function>nextval</function>
+        was used on in the current session. It is an error to call
+        <function>lastval</function> if <function>nextval</function>
+        has not yet been called in the current session.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><function>setval</function></term>
       <listitem>

src/backend/commands/sequence.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.122 2005/06/06 20:22:57 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.123 2005/06/07 07:08:34 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -24,6 +24,7 @@
 #include "utils/acl.h"
 #include "utils/builtins.h"
 #include "utils/resowner.h"
+#include "utils/syscache.h"
 
 
 /*
@@ -68,7 +69,13 @@ typedef SeqTableData *SeqTable;
 
 static SeqTable seqtab = NULL;	/* Head of list of SeqTable items */
 
+/*
+ * last_used_seq is updated by nextval() to point to the last used
+ * sequence.
+ */
+static SeqTableData *last_used_seq = NULL;
 
+static void acquire_share_lock(Relation seqrel, SeqTable seq);
 static void init_sequence(RangeVar *relation,
 			  SeqTable *p_elm, Relation *p_rel);
 static Form_pg_sequence read_info(SeqTable elm, Relation rel, Buffer *buf);
@@ -400,6 +407,7 @@ nextval(PG_FUNCTION_ARGS)
 
 	if (elm->last != elm->cached)		/* some numbers were cached */
 	{
+		last_used_seq = elm;
 		elm->last += elm->increment;
 		relation_close(seqrel, NoLock);
 		PG_RETURN_INT64(elm->last);
@@ -521,6 +529,8 @@ nextval(PG_FUNCTION_ARGS)
 	elm->last = result;			/* last returned number */
 	elm->cached = last;			/* last fetched number */
 
+	last_used_seq = elm;
+
 	START_CRIT_SECTION();
 
 	/* XLOG stuff */
@@ -602,6 +612,42 @@ currval(PG_FUNCTION_ARGS)
 	PG_RETURN_INT64(result);
 }
 
+Datum
+lastval(PG_FUNCTION_ARGS)
+{
+	Relation	seqrel;
+	int64		result;
+
+	if (last_used_seq == NULL)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("lastval is not yet defined in this session")));
+
+	/* Someone may have dropped the sequence since the last nextval() */
+	if (!SearchSysCacheExists(RELOID,
+							  ObjectIdGetDatum(last_used_seq->relid),
+							  0, 0, 0))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("lastval is not yet defined in this session")));
+
+	seqrel = relation_open(last_used_seq->relid, NoLock);
+	acquire_share_lock(seqrel, last_used_seq);
+
+	/* nextval() must have already been called for this sequence */
+	Assert(last_used_seq->increment != 0);
+
+	if (pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied for sequence %s",
+						RelationGetRelationName(seqrel))));
+
+	result = last_used_seq->last;
+	relation_close(seqrel, NoLock);
+	PG_RETURN_INT64(result);
+}
+
 /*
  * Main internal procedure that handles 2 & 3 arg forms of SETVAL.
  *
@@ -740,6 +786,41 @@ setval_and_iscalled(PG_FUNCTION_ARGS)
 }
 
 
+/*
+ * If we haven't touched the sequence already in this transaction,
+ * we need to acquire AccessShareLock.  We arrange for the lock to
+ * be owned by the top transaction, so that we don't need to do it
+ * more than once per xact.
+ */
+static void
+acquire_share_lock(Relation seqrel, SeqTable seq)
+{
+	TransactionId thisxid = GetTopTransactionId();
+
+	if (seq->xid != thisxid)
+	{
+		ResourceOwner currentOwner;
+
+		currentOwner = CurrentResourceOwner;
+		PG_TRY();
+		{
+			CurrentResourceOwner = TopTransactionResourceOwner;
+			LockRelation(seqrel, AccessShareLock);
+		}
+		PG_CATCH();
+		{
+			/* Ensure CurrentResourceOwner is restored on error */
+			CurrentResourceOwner = currentOwner;
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+		CurrentResourceOwner = currentOwner;
+
+		/* Flag that we have a lock in the current xact. */
+		seq->xid = thisxid;
+	}
+}
+
 /*
  * Given a relation name, open and lock the sequence.  p_elm and p_rel are
  * output parameters.
@@ -748,7 +829,6 @@ static void
 init_sequence(RangeVar *relation, SeqTable *p_elm, Relation *p_rel)
 {
 	Oid			relid = RangeVarGetRelid(relation, false);
-	TransactionId thisxid = GetTopTransactionId();
 	volatile SeqTable elm;
 	Relation	seqrel;
 
@@ -796,35 +876,7 @@ init_sequence(RangeVar *relation, SeqTable *p_elm, Relation *p_rel)
 		seqtab = elm;
 	}
 
-	/*
-	 * If we haven't touched the sequence already in this transaction,
-	 * we need to acquire AccessShareLock.  We arrange for the lock to
-	 * be owned by the top transaction, so that we don't need to do it
-	 * more than once per xact.
-	 */
-	if (elm->xid != thisxid)
-	{
-		ResourceOwner currentOwner;
-
-		currentOwner = CurrentResourceOwner;
-		PG_TRY();
-		{
-			CurrentResourceOwner = TopTransactionResourceOwner;
-
-			LockRelation(seqrel, AccessShareLock);
-		}
-		PG_CATCH();
-		{
-			/* Ensure CurrentResourceOwner is restored on error */
-			CurrentResourceOwner = currentOwner;
-			PG_RE_THROW();
-		}
-		PG_END_TRY();
-		CurrentResourceOwner = currentOwner;
-
-		/* Flag that we have a lock in the current xact. */
-		elm->xid = thisxid;
-	}
+	acquire_share_lock(seqrel, elm);
 
 	*p_elm = elm;
 	*p_rel = seqrel;

src/include/catalog/catversion.h

@@ -37,7 +37,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.272 2005/05/30 20:59:17 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.273 2005/06/07 07:08:34 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	200505302
+#define CATALOG_VERSION_NO	200506071
 
 #endif

src/include/catalog/pg_proc.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.363 2005/05/20 01:29:55 neilc Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_proc.h,v 1.364 2005/06/07 07:08:34 neilc Exp $
  *
  * NOTES
  *	  The script catalog/genbki.sh reads this file and generates .bki
@@ -3644,6 +3644,8 @@ DATA(insert OID = 2557 ( bool				   PGNSP PGUID 12 f f t f i 1  16 "23" _null_ _
 DESCR("convert int4 to boolean");
 DATA(insert OID = 2558 ( int4				   PGNSP PGUID 12 f f t f i 1  23 "16" _null_ _null_ _null_	bool_int4 - _null_ ));
 DESCR("convert boolean to int4");
+DATA(insert OID = 2559 ( lastval			   PGNSP PGUID 12 f f t f v 0 20 "" _null_ _null_ _null_	lastval - _null_ ));
+DESCR("current value from last used sequence");
 
 
 /*

src/include/commands/sequence.h

@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/sequence.h,v 1.31 2005/06/06 17:01:25 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/commands/sequence.h,v 1.32 2005/06/07 07:08:35 neilc Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -82,6 +82,7 @@ typedef struct xl_seq_rec
 
 extern Datum nextval(PG_FUNCTION_ARGS);
 extern Datum currval(PG_FUNCTION_ARGS);
+extern Datum lastval(PG_FUNCTION_ARGS);
 extern Datum setval(PG_FUNCTION_ARGS);
 extern Datum setval_and_iscalled(PG_FUNCTION_ARGS);
 

src/test/regress/expected/sequence.out

@@ -76,3 +76,62 @@ COMMENT ON SEQUENCE asdf IS 'won''t work';
 ERROR:  relation "asdf" does not exist
 COMMENT ON SEQUENCE sequence_test2 IS 'will work';
 COMMENT ON SEQUENCE sequence_test2 IS NULL;
+-- Test lastval()
+CREATE SEQUENCE seq;
+SELECT nextval('seq');
+ nextval 
+---------
+       1
+(1 row)
+
+SELECT lastval();
+ lastval 
+---------
+       1
+(1 row)
+
+SELECT setval('seq', 99);
+ setval 
+--------
+     99
+(1 row)
+
+SELECT lastval();
+ lastval 
+---------
+      99
+(1 row)
+
+CREATE SEQUENCE seq2;
+SELECT nextval('seq2');
+ nextval 
+---------
+       1
+(1 row)
+
+SELECT lastval();
+ lastval 
+---------
+       1
+(1 row)
+
+DROP SEQUENCE seq2;
+-- should fail
+SELECT lastval();
+ERROR:  lastval is not yet defined in this session
+CREATE USER seq_user;
+BEGIN;
+SET LOCAL SESSION AUTHORIZATION seq_user;
+CREATE SEQUENCE seq3;
+SELECT nextval('seq3');
+ nextval 
+---------
+       1
+(1 row)
+
+REVOKE ALL ON seq3 FROM seq_user;
+SELECT lastval();
+ERROR:  permission denied for sequence seq3
+ROLLBACK;
+DROP USER seq_user;
+DROP SEQUENCE seq;

src/test/regress/sql/sequence.sql

@@ -42,3 +42,30 @@ COMMENT ON SEQUENCE asdf IS 'won''t work';
 COMMENT ON SEQUENCE sequence_test2 IS 'will work';
 COMMENT ON SEQUENCE sequence_test2 IS NULL;
 
+-- Test lastval()
+CREATE SEQUENCE seq;
+SELECT nextval('seq');
+SELECT lastval();
+SELECT setval('seq', 99);
+SELECT lastval();
+
+CREATE SEQUENCE seq2;
+SELECT nextval('seq2');
+SELECT lastval();
+
+DROP SEQUENCE seq2;
+-- should fail
+SELECT lastval();
+
+CREATE USER seq_user;
+
+BEGIN;
+SET LOCAL SESSION AUTHORIZATION seq_user;
+CREATE SEQUENCE seq3;
+SELECT nextval('seq3');
+REVOKE ALL ON seq3 FROM seq_user;
+SELECT lastval();
+ROLLBACK;
+
+DROP USER seq_user;
+DROP SEQUENCE seq;