Function CteScanNext

src/backend/executor/nodeCtescan.c:30–139

---------------------------------------------------------------- * CteScanNext * * This is a workhorse for ExecCteScan * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static TupleTableSlot *
CteScanNext(CteScanState *node)
{
	EState	   *estate;
	ScanDirection dir;
	bool		forward;
	Tuplestorestate *tuplestorestate;
	bool		eof_tuplestore;
	TupleTableSlot *slot;

	/*
	 * get state info from node
	 */
	estate = node->ss.ps.state;
	dir = estate->es_direction;
	forward = ScanDirectionIsForward(dir);
	tuplestorestate = node->leader->cte_table;
	tuplestore_select_read_pointer(tuplestorestate, node->readptr);
	slot = node->ss.ss_ScanTupleSlot;

	/*
	 * If we are not at the end of the tuplestore, or are going backwards, try
	 * to fetch a tuple from tuplestore.
	 */
	eof_tuplestore = tuplestore_ateof(tuplestorestate);

	if (!forward && eof_tuplestore)
	{
		if (!node->leader->eof_cte)
		{
			/*
			 * When reversing direction at tuplestore EOF, the first
			 * gettupleslot call will fetch the last-added tuple; but we want
			 * to return the one before that, if possible. So do an extra
			 * fetch.
			 */
			if (!tuplestore_advance(tuplestorestate, forward))
				return NULL;	/* the tuplestore must be empty */
		}
		eof_tuplestore = false;
	}

	/*
	 * If we can fetch another tuple from the tuplestore, return it.
	 *
	 * Note: we have to use copy=true in the tuplestore_gettupleslot call,
	 * because we are sharing the tuplestore with other nodes that might write
	 * into the tuplestore before we get called again.
	 */
	if (!eof_tuplestore)
	{
		if (tuplestore_gettupleslot(tuplestorestate, forward, true, slot))
			return slot;
		if (forward)
			eof_tuplestore = true;
	}

	/*