Function show_tuple_split_keys

src/backend/commands/explain.c:3274–3311

* Show the Split key for an SplitTuple */

 * Show the Split key for an SplitTuple
 */
static void
show_tuple_split_keys(TupleSplitState *tstate, List *ancestors,
					  ExplainState *es)
{
	TupleSplit *plan = (TupleSplit *)tstate->ss.ps.plan;

	ancestors = lcons(tstate, ancestors);

	List	   *context;
	bool		useprefix;
	List	   *result = NIL;
	/* Set up deparsing context */
	context = set_deparse_context_plan(es->deparse_cxt,
									   (Plan *) plan,
									   ancestors);
	useprefix = (list_length(es->rtable) > 1 || es->verbose);

	StringInfoData buf;
	initStringInfo(&buf);

	ListCell *lc;
	foreach(lc, plan->dqa_expr_lst)
	{
		DQAExpr *dqa_expr = (DQAExpr *)lfirst(lc);
		result = lappend(result,
		                 deparse_expression((Node *) dqa_expr, context,
		                                    useprefix, true));
	}
	ExplainPropertyList("Split by Col", result, es);

	if (plan->numCols > 0)
		show_sort_group_keys(outerPlanState(tstate), "Group Key",
							 plan->numCols, 0, plan->grpColIdx,
							 NULL, NULL, NULL,
							 ancestors, es);

	ancestors = list_delete_first(ancestors);
}

/*
 * Show the grouping keys for an Agg node.