Function agg_retrieve_direct

src/backend/executor/nodeAgg.c:2379–2720

* ExecAgg for non-hashed case */

 * ExecAgg for non-hashed case
 */
static TupleTableSlot *
agg_retrieve_direct(AggState *aggstate)
{
	Agg		   *node = aggstate->phase->aggnode;
	ExprContext *econtext;
	ExprContext *tmpcontext;
	AggStatePerAgg peragg;
	AggStatePerGroup *pergroups;
	TupleTableSlot *outerslot;
	TupleTableSlot *firstSlot;
	TupleTableSlot *result;
	bool		hasGroupingSets = aggstate->phase->numsets > 0;
	int			numGroupingSets = Max(aggstate->phase->numsets, 1);
	int			currentSet;
	int			nextSetSize;
	int			numReset;
	int			i;

	/*
	 * get state info from node
	 *
	 * econtext is the per-output-tuple expression context
	 *
	 * tmpcontext is the per-input-tuple expression context
	 */
	econtext = aggstate->ss.ps.ps_ExprContext;
	tmpcontext = aggstate->tmpcontext;

	peragg = aggstate->peragg;
	pergroups = aggstate->pergroups;
	firstSlot = aggstate->ss.ss_ScanTupleSlot;

	/*
	 * We loop retrieving groups until we find one matching
	 * aggstate->ss.ps.qual
	 *
	 * For grouping sets, we have the invariant that aggstate->projected_set
	 * is either -1 (initial call) or the index (starting from 0) in
	 * gset_lengths for the group we just completed (either by projecting a
	 * row or by discarding it in the qual).
	 */
	while (!aggstate->agg_done)
	{
		/*
		 * Clear the per-output-tuple context for each group, as well as
		 * aggcontext (which contains any pass-by-ref transvalues of the old
		 * group).  Some aggregate functions store working state in child
		 * contexts; those now get reset automatically without us needing to
		 * do anything special.
		 *
		 * We use ReScanExprContext not just ResetExprContext because we want
		 * any registered shutdown callbacks to be called.  That allows
		 * aggregate functions to ensure they've cleaned up any non-memory
		 * resources.
		 */
		ReScanExprContext(econtext);

		/*