Function ExecBuildAggTrans

src/backend/executor/execExpr.c:3572–3911

* Build transition/combine function invocations for all aggregate transition * / combination function invocations in a grouping sets phase. This has to * invoke all sort based transitions in a phase (if doSort is true), all hash * based transitions (if doHash is true), or both (both true). * * The resulting expression will, for each set of transition values, first * check for filters, evalua

 * the array of AggStatePerGroup, and skip evaluation if so.
 */
ExprState *
ExecBuildAggTrans(AggState *aggstate, AggStatePerPhase phase,
				  bool doSort, bool doHash, bool nullcheck)
{
	ExprState  *state = makeNode(ExprState);
	PlanState  *parent = &aggstate->ss.ps;
	ExprEvalStep scratch = {0};
	LastAttnumInfo deform = {0, 0, 0};

	state->expr = (Expr *) aggstate;
	state->parent = parent;

	scratch.resvalue = &state->resvalue;
	scratch.resnull = &state->resnull;

	/*
	 * First figure out which slots, and how many columns from each, we're
	 * going to need.
	 */
	for (int transno = 0; transno < aggstate->numtrans; transno++)
	{
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];

		if (!bms_is_member(transno, aggstate->aggs_used))
			continue;
		get_last_attnums_walker((Node *) pertrans->aggref->aggdirectargs,
								&deform);
		get_last_attnums_walker((Node *) pertrans->aggref->args,
								&deform);
		get_last_attnums_walker((Node *) pertrans->aggref->aggorder,
								&deform);
		get_last_attnums_walker((Node *) pertrans->aggref->aggdistinct,
								&deform);
		get_last_attnums_walker((Node *) pertrans->aggref->aggfilter,
								&deform);

		if (aggstate->AggExprId_AttrNum > 0)
			deform.last_outer = Max(deform.last_outer,
									aggstate->AggExprId_AttrNum);
	}
	ExecPushExprSlots(state, &deform);

	/*
	 * Emit instructions for each transition value / grouping set combination.
	 */
	for (int transno = 0; transno < aggstate->numtrans; transno++)
	{
		AggStatePerTrans pertrans = &aggstate->pertrans[transno];
		FunctionCallInfo trans_fcinfo = pertrans->transfn_fcinfo;
		List	   *adjust_bailout = NIL;
		NullableDatum *strictargs = NULL;
		bool	   *strictnulls = NULL;
		int			argno;
		ListCell   *bail;
		if (!bms_is_member(transno, aggstate->aggs_used))
			continue;

		bool isCombine = DO_AGGSPLIT_COMBINE(pertrans->aggref->aggsplit);