ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
				  ParamListInfo params, QueryEnvironment *queryEnv,
				  QueryCompletion *qc)
{
	Query	   *query = castNode(Query, stmt->query);
	IntoClause *into = stmt->into;
	bool		is_matview = (into->viewQuery != NULL);
	DestReceiver *dest;
	Oid			save_userid = InvalidOid;
	int			save_sec_context = 0;
	int			save_nestlevel = 0;
	ObjectAddress address;
	List	   *rewritten;
	PlannedStmt *plan;
	QueryDesc  *queryDesc;

	if (stmt->if_not_exists)
	{
		Oid			nspid;
		Oid			oldrelid;

		nspid = RangeVarGetCreationNamespace(into->rel);

		oldrelid = get_relname_relid(into->rel->relname, nspid);
		if (OidIsValid(oldrelid))
		{
			/*
			 * The relation exists and IF NOT EXISTS has been specified.
			 *
			 * If we are in an extension script, insist that the pre-existing
			 * object be a member of the extension, to avoid security risks.
			 */
			ObjectAddressSet(address, RelationRelationId, oldrelid);
			checkMembershipInCurrentExtension(&address);

			/* OK to skip */
			ereport(NOTICE,
					(errcode(ERRCODE_DUPLICATE_TABLE),
					 errmsg("relation \"%s\" already exists, skipping",
							into->rel->relname)));
			return InvalidObjectAddress;
		}
	}

	/*
	 * Create the tuple receiver object and insert info it will need
	 */
	dest = CreateIntoRelDestReceiver(into);

	/*
	 * The contained Query could be a SELECT, or an EXECUTE utility command.
	 * If the latter, we just pass it off to ExecuteQuery.
	 */
	if (query->commandType == CMD_UTILITY &&
		IsA(query->utilityStmt, ExecuteStmt))
	{
		ExecuteStmt *estmt = castNode(ExecuteStmt, query->utilityStmt);

		Assert(!is_matview);	/* excluded by syntax */
		ExecuteQuery(pstate, estmt, into, params, dest, qc);

		/* get object address that intorel_startup saved for us */
		address = ((DR_intorel *) dest)->reladdr;

		return address;
	}
	Assert(query->commandType == CMD_SELECT);

	/*
	 * For materialized views, lock down security-restricted operations and
	 * arrange to make GUC variable changes local to this command.  This is
	 * not necessary for security, but this keeps the behavior similar to
	 * REFRESH MATERIALIZED VIEW.  Otherwise, one could create a materialized
	 * view not possible to refresh.
	 */
	if (is_matview)
	{
		GetUserIdAndSecContext(&save_userid, &save_sec_context);
		SetUserIdAndSecContext(save_userid,
							   save_sec_context | SECURITY_RESTRICTED_OPERATION);
		save_nestlevel = NewGUCNestLevel();
	}

	if (into->skipData)
	{
		/*
		 * If WITH NO DATA was specified, do not go through the rewriter,
		 * planner and executor.  Just define the relation using a code path
		 * similar to CREATE VIEW.  This avoids dump/restore problems stemming
		 * from running the planner before all dependencies are set up.
		 */
		address = create_ctas_nodata(query->targetList, into);
	}
	else
	{
		/*
		 * Parse analysis was done already, but we still have to run the rule
		 * rewriter.  We do not do AcquireRewriteLocks: we assume the query
		 * either came straight from the parser, or suitable locks were
		 * acquired by plancache.c.
		 *
		 * Because the rewriter and planner tend to scribble on the input, we
		 * make a preliminary copy of the source querytree.  This prevents
		 * problems in the case that CTAS is in a portal or plpgsql function
		 * and is executed repeatedly.  (See also the same hack in EXPLAIN and
		 * PREPARE.)
		 */
		rewritten = QueryRewrite(copyObject(query));

		/* SELECT should never rewrite to more or less than one SELECT query */
		if (list_length(rewritten) != 1)
			elog(ERROR, "unexpected rewrite result for %s",
				 is_matview ? "CREATE MATERIALIZED VIEW" :
				 "CREATE TABLE AS SELECT");
		query = linitial_node(Query, rewritten);
		Assert(query->commandType == CMD_SELECT);

		/* plan the query */
		plan = pg_plan_query(query, pstate->p_sourcetext,
							 CURSOR_OPT_PARALLEL_OK, params);

		/*
		 * Use a snapshot with an updated command ID to ensure this query sees
		 * results of any previously executed queries.  (This could only
		 * matter if the planner executed an allegedly-stable function that
		 * changed the database contents, but let's do it anyway to be
		 * parallel to the EXPLAIN code path.)
		 */
		PushCopiedSnapshot(GetActiveSnapshot());
		UpdateActiveSnapshotCommandId();

		/* Create a QueryDesc, redirecting output to our tuple receiver */
		queryDesc = CreateQueryDesc(plan, pstate->p_sourcetext,
									GetActiveSnapshot(), InvalidSnapshot,
									dest, params, queryEnv, 0);

		/* call ExecutorStart to prepare the plan for execution */
		ExecutorStart(queryDesc, GetIntoRelEFlags(into));

		/* run the plan to completion */
		ExecutorRun(queryDesc, ForwardScanDirection, 0L, true);

		/* save the rowcount if we're given a qc to fill */
		if (qc)
			SetQueryCompletion(qc, CMDTAG_SELECT, queryDesc->estate->es_processed);

		/* get object address that intorel_startup saved for us */
		address = ((DR_intorel *) dest)->reladdr;

		/* and clean up */
		ExecutorFinish(queryDesc);
		ExecutorEnd(queryDesc);

		FreeQueryDesc(queryDesc);

		PopActiveSnapshot();
	}

	if (is_matview)
	{
		/* Roll back any GUC changes */
		AtEOXact_GUC(false, save_nestlevel);

		/* Restore userid and security context */
		SetUserIdAndSecContext(save_userid, save_sec_context);
	}

	return address;
}
ExecCreateTableAs(ParseState *pstate, CreateTableAsStmt *stmt,
				  ParamListInfo params, QueryEnvironment *queryEnv,
				  QueryCompletion *qc)
{
	Query	   *query = castNode(Query, stmt->query);
	IntoClause *into = stmt->into;
	bool		is_matview = (into->viewQuery != NULL);
	DestReceiver *dest;
	Oid			save_userid = InvalidOid;
	int			save_sec_context = 0;
	int			save_nestlevel = 0;
	ObjectAddress address;
	List	   *rewritten;
	PlannedStmt *plan;
	QueryDesc  *queryDesc;

	if (stmt->if_not_exists)
	{
		Oid			nspid;
		Oid			oldrelid;

		nspid = RangeVarGetCreationNamespace(into->rel);

		oldrelid = get_relname_relid(into->rel->relname, nspid);
		if (OidIsValid(oldrelid))
		{
			 
			ObjectAddressSet(address, RelationRelationId, oldrelid);
			checkMembershipInCurrentExtension(&address);

			 
			ereport(NOTICE,
					(errcode(ERRCODE_DUPLICATE_TABLE),
					 errmsg("relation \"%s\" already exists, skipping",
							into->rel->relname)));
			return InvalidObjectAddress;
		}
	}

	 
	dest = CreateIntoRelDestReceiver(into);

	 
	if (query->commandType == CMD_UTILITY &&
		IsA(query->utilityStmt, ExecuteStmt))
	{
		ExecuteStmt *estmt = castNode(ExecuteStmt, query->utilityStmt);

		Assert(!is_matview);	 
		ExecuteQuery(pstate, estmt, into, params, dest, qc);

		 
		address = ((DR_intorel *) dest)->reladdr;

		return address;
	}
	Assert(query->commandType == CMD_SELECT);

	 
	if (is_matview)
	{
		GetUserIdAndSecContext(&save_userid, &save_sec_context);
		SetUserIdAndSecContext(save_userid,
							   save_sec_context | SECURITY_RESTRICTED_OPERATION);
		save_nestlevel = NewGUCNestLevel();
	}

	if (into->skipData)
	{
		 
		address = create_ctas_nodata(query->targetList, into);
	}
	else
	{
		 
		rewritten = QueryRewrite(copyObject(query));

		 
		if (list_length(rewritten) != 1)
			elog(ERROR, "unexpected rewrite result for %s",
				 is_matview ? "CREATE MATERIALIZED VIEW" :
				 "CREATE TABLE AS SELECT");
		query = linitial_node(Query, rewritten);
		Assert(query->commandType == CMD_SELECT);

		 
		plan = pg_plan_query(query, pstate->p_sourcetext,
							 CURSOR_OPT_PARALLEL_OK, params);

		 
		PushCopiedSnapshot(GetActiveSnapshot());
		UpdateActiveSnapshotCommandId();

		 
		queryDesc = CreateQueryDesc(plan, pstate->p_sourcetext,
									GetActiveSnapshot(), InvalidSnapshot,
									dest, params, queryEnv, 0);

		 
		ExecutorStart(queryDesc, GetIntoRelEFlags(into));

		 
		ExecutorRun(queryDesc, ForwardScanDirection, 0L, true);

		 
		if (qc)
			SetQueryCompletion(qc, CMDTAG_SELECT, queryDesc->estate->es_processed);

		 
		address = ((DR_intorel *) dest)->reladdr;

		 
		ExecutorFinish(queryDesc);
		ExecutorEnd(queryDesc);

		FreeQueryDesc(queryDesc);

		PopActiveSnapshot();
	}

	if (is_matview)
	{
		 
		AtEOXact_GUC(false, save_nestlevel);

		 
		SetUserIdAndSecContext(save_userid, save_sec_context);
	}

	return address;
}