Function ExplainPreScanNode

src/backend/commands/explain.c:1452–1510

* ExplainPreScanNode - * Prescan the planstate tree to identify which RTEs are referenced * * Adds the relid of each referenced RTE to *rels_used. The result controls * which RTEs are assigned aliases by select_rtable_names_for_explain. * This ensures that we don't confusingly assign un-suffixed aliases to RTEs * that never appear in the EXPLAIN output (such as inheritance parents). */

 * that never appear in the EXPLAIN output (such as inheritance parents).
 */
static bool
ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
{
	Plan	   *plan = planstate->plan;

	switch (nodeTag(plan))
	{
		case T_SeqScan:
		case T_SampleScan:
		case T_IndexScan:
		case T_IndexOnlyScan:
		case T_BitmapHeapScan:
		case T_DynamicBitmapHeapScan:
		case T_TidScan:
		case T_TidRangeScan:
		case T_SubqueryScan:
		case T_FunctionScan:
		case T_TableFuncScan:
		case T_ValuesScan:
		case T_CteScan:
		case T_NamedTuplestoreScan:
		case T_WorkTableScan:
		case T_DynamicSeqScan:
		case T_DynamicIndexScan:
		case T_DynamicIndexOnlyScan:
		case T_ShareInputScan:
			*rels_used = bms_add_member(*rels_used,
										((Scan *) plan)->scanrelid);
			break;
		case T_ForeignScan:
		case T_DynamicForeignScan:
			*rels_used = bms_add_members(*rels_used,
										 ((ForeignScan *) plan)->fs_relids);
			break;
		case T_CustomScan:
			*rels_used = bms_add_members(*rels_used,
										 ((CustomScan *) plan)->custom_relids);
			break;
		case T_ModifyTable:
			*rels_used = bms_add_member(*rels_used,
										((ModifyTable *) plan)->nominalRelation);
			if (((ModifyTable *) plan)->exclRelRTI)
				*rels_used = bms_add_member(*rels_used,
											((ModifyTable *) plan)->exclRelRTI);
			break;
		case T_Append:
			*rels_used = bms_add_members(*rels_used,
										 ((Append *) plan)->apprelids);
			break;
		case T_MergeAppend:
			*rels_used = bms_add_members(*rels_used,
										 ((MergeAppend *) plan)->apprelids);
			break;
		default:
			break;
	}

	return planstate_tree_walker(planstate, ExplainPreScanNode, rels_used);