Function create_minmaxagg_plan

src/backend/optimizer/plan/createplan.c:2826–2890

* create_minmaxagg_plan * * Create a Result plan for 'best_path' and (recursively) plans * for its subpaths. */

 *	  for its subpaths.
 */
static Result *
create_minmaxagg_plan(PlannerInfo *root, MinMaxAggPath *best_path)
{
	Result	   *plan;
	List	   *tlist;
	ListCell   *lc;

	/* Prepare an InitPlan for each aggregate's subquery. */
	foreach(lc, best_path->mmaggregates)
	{
		MinMaxAggInfo *mminfo = (MinMaxAggInfo *) lfirst(lc);
		PlannerInfo *subroot = mminfo->subroot;
		Query	   *subparse = subroot->parse;
		Plan	   *plan;

		mminfo->path = cdbllize_adjust_init_plan_path(subroot, mminfo->path);

		/*
		 * Generate the plan for the subquery. We already have a Path, but we
		 * have to convert it to a Plan and attach a LIMIT node above it.
		 * Since we are entering a different planner context (subroot),
		 * recurse to create_plan not create_plan_recurse.
		 */
		plan = create_plan(subroot, mminfo->path, root->curSlice);

		/* Decorate the top node of the plan with a Flow node. */
		plan->flow = cdbpathtoplan_create_flow(root, mminfo->path->locus);

		plan = (Plan *) make_limit(plan,
								   subparse->limitOffset,
								   subparse->limitCount,
								   subparse->limitOption,
								   0, NULL, NULL, NULL);
		plan->flow = plan->lefttree->flow;

		/* Must apply correct cost/width data to Limit node */
		plan->startup_cost = mminfo->path->startup_cost;
		plan->total_cost = mminfo->pathcost;
		plan->plan_rows = 1;
		plan->plan_width = mminfo->path->pathtarget->width;
		plan->parallel_aware = false;
		plan->parallel_safe = mminfo->path->parallel_safe;

		/* Convert the plan into an InitPlan in the outer query. */
		SS_make_initplan_from_plan(root, subroot, plan, root->curSlice, mminfo->param, false);
	}

	/* Generate the output plan --- basically just a Result */
	tlist = build_path_tlist(root, &best_path->path);

	plan = make_result(tlist, (Node *) best_path->quals, NULL);

	copy_generic_path_info(&plan->plan, (Path *) best_path);

	/*
	 * During setrefs.c, we'll need to replace references to the Agg nodes
	 * with InitPlan output params.  (We can't just do that locally in the
	 * MinMaxAgg node, because path nodes above here may have Agg references