Make ALTER .. SET SCHEMA do nothing, instead of throwing an ERROR.

This was already true for CREATE EXTENSION, but historically has not
been true for other object types.  Therefore, this is a backward
incompatibility.  Per discussion on pgsql-hackers, everyone seems to
agree that the new behavior is better.

Marti Raudsepp, reviewed by Haribabu Kommi and myself

src/backend/catalog/namespace.c

@@ -2769,24 +2769,13 @@ LookupCreationNamespace(const char *nspname)
 /*
  * Common checks on switching namespaces.
  *
- * We complain if (1) the old and new namespaces are the same, (2) either the
- * old or new namespaces is a temporary schema (or temporary toast schema), or
- * (3) either the old or new namespaces is the TOAST schema.
+ * We complain if (1) either the old or new namespaces is a temporary schema
+ * (or temporary toast schema), or (3) either the old or new namespaces is the
+ * TOAST schema.
  */
 void
-CheckSetNamespace(Oid oldNspOid, Oid nspOid, Oid classid, Oid objid)
+CheckSetNamespace(Oid oldNspOid, Oid nspOid)
 {
-	if (oldNspOid == nspOid)
-		ereport(ERROR,
-				(classid == RelationRelationId ?
-				 errcode(ERRCODE_DUPLICATE_TABLE) :
-				 classid == ProcedureRelationId ?
-				 errcode(ERRCODE_DUPLICATE_FUNCTION) :
-				 errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("%s is already in schema \"%s\"",
-						getObjectDescriptionOids(classid, objid),
-						get_namespace_name(nspOid))));
-
 	/* disallow renaming into or out of temp schemas */
 	if (isAnyTempNamespace(nspOid) || isAnyTempNamespace(oldNspOid))
 		ereport(ERROR,

src/backend/catalog/pg_constraint.c

@@ -726,7 +726,8 @@ AlterConstraintNamespaces(Oid ownerId, Oid oldNspId,
 		if (object_address_present(&thisobj, objsMoved))
 			continue;
 
-		if (conform->connamespace == oldNspId)
+		/* Don't update if the object is already part of the namespace */
+		if (conform->connamespace == oldNspId && oldNspId != newNspId)
 		{
 			tup = heap_copytuple(tup);
 			conform = (Form_pg_constraint) GETSTRUCT(tup);

src/backend/commands/alter.c

@@ -592,8 +592,18 @@ AlterObjectNamespace_internal(Relation rel, Oid objid, Oid nspOid)
 	Assert(!isnull);
 	oldNspOid = DatumGetObjectId(namespace);
 
+	/*
+	 * If the object is already in the correct namespace, we don't need
+	 * to do anything except fire the object access hook.
+	 */
+	if (oldNspOid == nspOid)
+	{
+		InvokeObjectPostAlterHook(classId, objid, 0);
+		return oldNspOid;
+	}
+
 	/* Check basic namespace related issues */
-	CheckSetNamespace(oldNspOid, nspOid, classId, objid);
+	CheckSetNamespace(oldNspOid, nspOid);
 
 	/* Permission checks ... superusers can always do it */
 	if (!superuser())

src/backend/commands/tablecmds.c

@@ -11350,7 +11350,7 @@ AlterTableNamespace(AlterObjectSchemaStmt *stmt, Oid *oldschema)
 	nspOid = RangeVarGetAndCheckCreationNamespace(newrv, NoLock, NULL);
 
 	/* common checks on switching namespaces */
-	CheckSetNamespace(oldNspOid, nspOid, RelationRelationId, relid);
+	CheckSetNamespace(oldNspOid, nspOid);
 
 	objsMoved = new_object_addresses();
 	AlterTableNamespaceInternal(rel, oldNspOid, nspOid, objsMoved);
@@ -11418,6 +11418,7 @@ AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
 	HeapTuple	classTup;
 	Form_pg_class classForm;
 	ObjectAddress thisobj;
+	bool		already_done = false;
 
 	classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relOid));
 	if (!HeapTupleIsValid(classTup))
@@ -11431,9 +11432,12 @@ AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
 	thisobj.objectSubId = 0;
 
 	/*
-	 * Do nothing when there's nothing to do.
+	 * If the object has already been moved, don't move it again.  If it's
+	 * already in the right place, don't move it, but still fire the object
+	 * access hook.
 	 */
-	if (!object_address_present(&thisobj, objsMoved))
+	already_done = object_address_present(&thisobj, objsMoved);
+	if (!already_done && oldNspOid != newNspOid)
 	{
 		/* check for duplicate name (more friendly than unique-index failure) */
 		if (get_relname_relid(NameStr(classForm->relname),
@@ -11459,7 +11463,9 @@ AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
 								newNspOid) != 1)
 			elog(ERROR, "failed to change schema dependency for relation \"%s\"",
 				 NameStr(classForm->relname));
-
+	}
+	if (!already_done)
+	{
 		add_exact_object_address(&thisobj, objsMoved);
 
 		InvokeObjectPostAlterHook(RelationRelationId, relOid, 0);

src/backend/commands/typecmds.c

@@ -3520,18 +3520,22 @@ AlterTypeNamespaceInternal(Oid typeOid, Oid nspOid,
 	oldNspOid = typform->typnamespace;
 	arrayOid = typform->typarray;
 
-	/* common checks on switching namespaces */
-	CheckSetNamespace(oldNspOid, nspOid, TypeRelationId, typeOid);
+	/* If the type is already there, we scan skip these next few checks. */
+	if (oldNspOid != nspOid)
+	{
+		/* common checks on switching namespaces */
+		CheckSetNamespace(oldNspOid, nspOid);
 
-	/* check for duplicate name (more friendly than unique-index failure) */
-	if (SearchSysCacheExists2(TYPENAMENSP,
-							  CStringGetDatum(NameStr(typform->typname)),
-							  ObjectIdGetDatum(nspOid)))
-		ereport(ERROR,
-				(errcode(ERRCODE_DUPLICATE_OBJECT),
-				 errmsg("type \"%s\" already exists in schema \"%s\"",
-						NameStr(typform->typname),
-						get_namespace_name(nspOid))));
+		/* check for duplicate name (more friendly than unique-index failure) */
+		if (SearchSysCacheExists2(TYPENAMENSP,
+								  CStringGetDatum(NameStr(typform->typname)),
+								  ObjectIdGetDatum(nspOid)))
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("type \"%s\" already exists in schema \"%s\"",
+							NameStr(typform->typname),
+							get_namespace_name(nspOid))));
+	}
 
 	/* Detect whether type is a composite type (but not a table rowtype) */
 	isCompositeType =
@@ -3547,13 +3551,16 @@ AlterTypeNamespaceInternal(Oid typeOid, Oid nspOid,
 						format_type_be(typeOid)),
 				 errhint("Use ALTER TABLE instead.")));
 
-	/* OK, modify the pg_type row */
+	if (oldNspOid != nspOid)
+	{
+		/* OK, modify the pg_type row */
 
-	/* tup is a copy, so we can scribble directly on it */
-	typform->typnamespace = nspOid;
+		/* tup is a copy, so we can scribble directly on it */
+		typform->typnamespace = nspOid;
 
-	simple_heap_update(rel, &tup->t_self, tup);
-	CatalogUpdateIndexes(rel, tup);
+		simple_heap_update(rel, &tup->t_self, tup);
+		CatalogUpdateIndexes(rel, tup);
+	}
 
 	/*
 	 * Composite types have pg_class entries.
@@ -3592,7 +3599,8 @@ AlterTypeNamespaceInternal(Oid typeOid, Oid nspOid,
 	 * Update dependency on schema, if any --- a table rowtype has not got
 	 * one, and neither does an implicit array.
 	 */
-	if ((isCompositeType || typform->typtype != TYPTYPE_COMPOSITE) &&
+	if (oldNspOid != nspOid &&
+		(isCompositeType || typform->typtype != TYPTYPE_COMPOSITE) &&
 		!isImplicitArray)
 		if (changeDependencyFor(TypeRelationId, typeOid,
 								NamespaceRelationId, oldNspOid, nspOid) != 1)

src/include/catalog/namespace.h

@@ -112,8 +112,7 @@ extern Oid	LookupExplicitNamespace(const char *nspname, bool missing_ok);
 extern Oid	get_namespace_oid(const char *nspname, bool missing_ok);
 
 extern Oid	LookupCreationNamespace(const char *nspname);
-extern void CheckSetNamespace(Oid oldNspOid, Oid nspOid, Oid classid,
-				  Oid objid);
+extern void CheckSetNamespace(Oid oldNspOid, Oid nspOid);
 extern Oid	QualifiedNameGetCreationNamespace(List *names, char **objname_p);
 extern RangeVar *makeRangeVarFromNameList(List *names);
 extern char *NameListToString(List *names);

src/test/regress/expected/alter_generic.out

@@ -40,6 +40,7 @@ ALTER FUNCTION alt_func1(int) RENAME TO alt_func3;  -- OK
 ALTER FUNCTION alt_func2(int) OWNER TO regtest_alter_user2;  -- failed (no role membership)
 ERROR:  must be member of role "regtest_alter_user2"
 ALTER FUNCTION alt_func2(int) OWNER TO regtest_alter_user3;  -- OK
+ALTER FUNCTION alt_func2(int) SET SCHEMA alt_nsp1;  -- OK, already there
 ALTER FUNCTION alt_func2(int) SET SCHEMA alt_nsp2;  -- OK
 ALTER AGGREGATE alt_agg1(int) RENAME TO alt_agg2;   -- failed (name conflict)
 ERROR:  function alt_agg2(integer) already exists in schema "alt_nsp1"

src/test/regress/expected/alter_table.out

@@ -2133,6 +2133,7 @@ create text search template alter1.tmpl(init = dsimple_init, lexize = dsimple_le
 create text search dictionary alter1.dict(template = alter1.tmpl);
 insert into alter1.t1(f2) values(11);
 insert into alter1.t1(f2) values(12);
+alter table alter1.t1 set schema alter1; -- no-op, same schema
 alter table alter1.t1 set schema alter2;
 alter table alter1.v1 set schema alter2;
 alter function alter1.plus1(int) set schema alter2;
@@ -2141,6 +2142,7 @@ alter operator class alter1.ctype_hash_ops using hash set schema alter2;
 alter operator family alter1.ctype_hash_ops using hash set schema alter2;
 alter operator alter1.=(alter1.ctype, alter1.ctype) set schema alter2;
 alter function alter1.same(alter1.ctype, alter1.ctype) set schema alter2;
+alter type alter1.ctype set schema alter1; -- no-op, same schema
 alter type alter1.ctype set schema alter2;
 alter conversion alter1.ascii_to_utf8 set schema alter2;
 alter text search parser alter1.prs set schema alter2;
@@ -2567,9 +2569,8 @@ ALTER TABLE new_system_table SET SCHEMA pg_catalog;
 -- XXX: it's currently impossible to move relations out of pg_catalog
 ALTER TABLE new_system_table SET SCHEMA public;
 ERROR:  cannot remove dependency on schema pg_catalog because it is a system object
--- move back, will currently error out, already there
+-- move back, will be ignored -- already there
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
-ERROR:  table new_system_table is already in schema "pg_catalog"
 ALTER TABLE new_system_table RENAME TO old_system_table;
 CREATE INDEX old_system_table__othercol ON old_system_table (othercol);
 INSERT INTO old_system_table(othercol) VALUES ('somedata'), ('otherdata');

src/test/regress/sql/alter_generic.sql

@@ -44,6 +44,7 @@ ALTER FUNCTION alt_func1(int) RENAME TO alt_func2;  -- failed (name conflict)
 ALTER FUNCTION alt_func1(int) RENAME TO alt_func3;  -- OK
 ALTER FUNCTION alt_func2(int) OWNER TO regtest_alter_user2;  -- failed (no role membership)
 ALTER FUNCTION alt_func2(int) OWNER TO regtest_alter_user3;  -- OK
+ALTER FUNCTION alt_func2(int) SET SCHEMA alt_nsp1;  -- OK, already there
 ALTER FUNCTION alt_func2(int) SET SCHEMA alt_nsp2;  -- OK
 
 ALTER AGGREGATE alt_agg1(int) RENAME TO alt_agg2;   -- failed (name conflict)

src/test/regress/sql/alter_table.sql

@@ -1465,6 +1465,7 @@ create text search dictionary alter1.dict(template = alter1.tmpl);
 insert into alter1.t1(f2) values(11);
 insert into alter1.t1(f2) values(12);
 
+alter table alter1.t1 set schema alter1; -- no-op, same schema
 alter table alter1.t1 set schema alter2;
 alter table alter1.v1 set schema alter2;
 alter function alter1.plus1(int) set schema alter2;
@@ -1473,6 +1474,7 @@ alter operator class alter1.ctype_hash_ops using hash set schema alter2;
 alter operator family alter1.ctype_hash_ops using hash set schema alter2;
 alter operator alter1.=(alter1.ctype, alter1.ctype) set schema alter2;
 alter function alter1.same(alter1.ctype, alter1.ctype) set schema alter2;
+alter type alter1.ctype set schema alter1; -- no-op, same schema
 alter type alter1.ctype set schema alter2;
 alter conversion alter1.ascii_to_utf8 set schema alter2;
 alter text search parser alter1.prs set schema alter2;
@@ -1704,7 +1706,7 @@ ALTER TABLE new_system_table SET SCHEMA pg_catalog;
 
 -- XXX: it's currently impossible to move relations out of pg_catalog
 ALTER TABLE new_system_table SET SCHEMA public;
--- move back, will currently error out, already there
+-- move back, will be ignored -- already there
 ALTER TABLE new_system_table SET SCHEMA pg_catalog;
 ALTER TABLE new_system_table RENAME TO old_system_table;
 CREATE INDEX old_system_table__othercol ON old_system_table (othercol);