1 files changed, 115 insertions, 2 deletions

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index adefc5471a3..19ffcc2cacb 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -107,6 +107,11 @@ static void show_sort_group_keys(PlanState *planstate, const char *qlabel,
 								 List *ancestors, ExplainState *es);
 static void show_sortorder_options(StringInfo buf, Node *sortexpr,
 								   Oid sortOperator, Oid collation, bool nullsFirst);
+static void show_window_def(WindowAggState *planstate,
+							List *ancestors, ExplainState *es);
+static void show_window_keys(StringInfo buf, PlanState *planstate,
+							 int nkeys, AttrNumber *keycols,
+							 List *ancestors, ExplainState *es);
 static void show_storage_info(char *maxStorageType, int64 maxSpaceUsed,
 							  ExplainState *es);
 static void show_tablesample(TableSampleClause *tsc, PlanState *planstate,
@@ -2333,12 +2338,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
 										   planstate, es);
 			break;
 		case T_WindowAgg:
+			show_window_def(castNode(WindowAggState, planstate), ancestors, es);
+			show_upper_qual(((WindowAgg *) plan)->runConditionOrig,
+							"Run Condition", planstate, ancestors, es);
 			show_upper_qual(plan->qual, "Filter", planstate, ancestors, es);
 			if (plan->qual)
 				show_instrumentation_count("Rows Removed by Filter", 1,
 										   planstate, es);
-			show_upper_qual(((WindowAgg *) plan)->runConditionOrig,
-							"Run Condition", planstate, ancestors, es);
 			show_windowagg_info(castNode(WindowAggState, planstate), es);
 			break;
 		case T_Group:
@@ -3008,6 +3014,113 @@ show_sortorder_options(StringInfo buf, Node *sortexpr,
 }
 
 /*
+ * Show the window definition for a WindowAgg node.
+ */
+static void
+show_window_def(WindowAggState *planstate, List *ancestors, ExplainState *es)
+{
+	WindowAgg  *wagg = (WindowAgg *) planstate->ss.ps.plan;
+	StringInfoData wbuf;
+	bool		needspace = false;
+
+	initStringInfo(&wbuf);
+	appendStringInfo(&wbuf, "%s AS (", quote_identifier(wagg->winname));
+
+	/* The key columns refer to the tlist of the child plan */
+	ancestors = lcons(wagg, ancestors);
+	if (wagg->partNumCols > 0)
+	{
+		appendStringInfoString(&wbuf, "PARTITION BY ");
+		show_window_keys(&wbuf, outerPlanState(planstate),
+						 wagg->partNumCols, wagg->partColIdx,
+						 ancestors, es);
+		needspace = true;
+	}
+	if (wagg->ordNumCols > 0)
+	{
+		if (needspace)
+			appendStringInfoChar(&wbuf, ' ');
+		appendStringInfoString(&wbuf, "ORDER BY ");
+		show_window_keys(&wbuf, outerPlanState(planstate),
+						 wagg->ordNumCols, wagg->ordColIdx,
+						 ancestors, es);
+		needspace = true;
+	}
+	ancestors = list_delete_first(ancestors);
+	if (wagg->frameOptions & FRAMEOPTION_NONDEFAULT)
+	{
+		List	   *context;
+		bool		useprefix;
+		char	   *framestr;
+
+		/* Set up deparsing context for possible frame expressions */
+		context = set_deparse_context_plan(es->deparse_cxt,
+										   (Plan *) wagg,
+										   ancestors);
+		useprefix = (es->rtable_size > 1 || es->verbose);
+		framestr = get_window_frame_options_for_explain(wagg->frameOptions,
+														wagg->startOffset,
+														wagg->endOffset,
+														context,
+														useprefix);
+		if (needspace)
+			appendStringInfoChar(&wbuf, ' ');
+		appendStringInfoString(&wbuf, framestr);
+		pfree(framestr);
+	}
+	appendStringInfoChar(&wbuf, ')');
+	ExplainPropertyText("Window", wbuf.data, es);
+	pfree(wbuf.data);
+}
+
+/*
+ * Append the keys of a window's PARTITION BY or ORDER BY clause to buf.
+ * We can't use show_sort_group_keys for this because that's too opinionated
+ * about how the result will be displayed.
+ * Note that the "planstate" node should be the WindowAgg's child.
+ */
+static void
+show_window_keys(StringInfo buf, PlanState *planstate,
+				 int nkeys, AttrNumber *keycols,
+				 List *ancestors, ExplainState *es)
+{
+	Plan	   *plan = planstate->plan;
+	List	   *context;
+	bool		useprefix;
+
+	/* Set up deparsing context */
+	context = set_deparse_context_plan(es->deparse_cxt,
+									   plan,
+									   ancestors);
+	useprefix = (es->rtable_size > 1 || es->verbose);
+
+	for (int keyno = 0; keyno < nkeys; keyno++)
+	{
+		/* find key expression in tlist */
+		AttrNumber	keyresno = keycols[keyno];
+		TargetEntry *target = get_tle_by_resno(plan->targetlist,
+											   keyresno);
+		char	   *exprstr;
+
+		if (!target)
+			elog(ERROR, "no tlist entry for key %d", keyresno);
+		/* Deparse the expression, showing any top-level cast */
+		exprstr = deparse_expression((Node *) target->expr, context,
+									 useprefix, true);
+		if (keyno > 0)
+			appendStringInfoString(buf, ", ");
+		appendStringInfoString(buf, exprstr);
+		pfree(exprstr);
+
+		/*
+		 * We don't attempt to provide sort order information because
+		 * WindowAgg carries equality operators not comparison operators;
+		 * compare show_agg_keys.
+		 */
+	}
+}
+
+/*
  * Show information on storage method and maximum memory/disk space used.
  */
 static void