From a78feec9bf7b08c644c2b3089b2de9237d4fcd9e Mon Sep 17 00:00:00 2001
From: Tatsuo Ishii <ishii@postgresql.org>
Date: Sat, 22 Apr 2023 17:00:06 +0900
Subject: [PATCH v1 3/3] Implement IGNORE or RESPECT NULLS executor and window
 functions part.

---
 src/backend/executor/nodeWindowAgg.c | 11 ++++++++++
 src/backend/utils/adt/windowfuncs.c  | 30 +++++++++++++++++++++++++---
 src/include/windowapi.h              |  2 ++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 3ac581a711..7e2affb12c 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -69,6 +69,7 @@ typedef struct WindowObjectData
 	int			readptr;		/* tuplestore read pointer for this fn */
 	int64		markpos;		/* row that markptr is positioned on */
 	int64		seekpos;		/* row that readptr is positioned on */
+	WindowFunc	*wfunc;			/* WindowFunc of this function */
 } WindowObjectData;
 
 /*
@@ -2617,6 +2618,7 @@ ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
 			winobj->winstate = winstate;
 			winobj->argstates = wfuncstate->args;
 			winobj->localmem = NULL;
+			winobj->wfunc = wfunc;
 			perfuncstate->winobj = winobj;
 
 			/* It's a real window function, so set up to call it. */
@@ -3620,3 +3622,12 @@ WinGetFuncArgCurrent(WindowObject winobj, int argno, bool *isnull)
 	return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
 						econtext, isnull);
 }
+
+/*
+ * Return current WindowFunc
+ */
+WindowFunc	*
+WinGetWindowFunc(WindowObject winobj)
+{
+	return winobj->wfunc;
+}
diff --git a/src/backend/utils/adt/windowfuncs.c b/src/backend/utils/adt/windowfuncs.c
index b87a624fb2..919295ba13 100644
--- a/src/backend/utils/adt/windowfuncs.c
+++ b/src/backend/utils/adt/windowfuncs.c
@@ -693,6 +693,7 @@ window_nth_value(PG_FUNCTION_ARGS)
 	bool		const_offset;
 	Datum		result;
 	bool		isnull;
+	bool		isout;
 	int32		nth;
 
 	nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
@@ -705,9 +706,32 @@ window_nth_value(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTH_VALUE),
 				 errmsg("argument of nth_value must be greater than zero")));
 
-	result = WinGetFuncArgInFrame(winobj, 0,
-								  nth - 1, WINDOW_SEEK_HEAD, const_offset,
-								  &isnull, NULL);
+	if (WinGetWindowFunc(winobj)->ignorenulls)
+	{
+		int		i, n;
+
+		i = n = 0;
+
+		for (;;)
+		{
+			result = WinGetFuncArgInFrame(winobj, 0,
+										  i++, WINDOW_SEEK_HEAD, false,
+										  &isnull, &isout);
+			if (isout)
+				break;
+
+			if (!isnull)
+			{
+				if (n == nth - 1)
+					break;
+				n++;
+			}
+		}
+	}
+	else
+		result = WinGetFuncArgInFrame(winobj, 0,
+									  nth - 1, WINDOW_SEEK_HEAD, const_offset,
+									  &isnull, NULL);
 	if (isnull)
 		PG_RETURN_NULL();
 
diff --git a/src/include/windowapi.h b/src/include/windowapi.h
index b8c2c565d1..64f7d4c84d 100644
--- a/src/include/windowapi.h
+++ b/src/include/windowapi.h
@@ -61,4 +61,6 @@ extern Datum WinGetFuncArgInFrame(WindowObject winobj, int argno,
 extern Datum WinGetFuncArgCurrent(WindowObject winobj, int argno,
 								  bool *isnull);
 
+extern WindowFunc	*WinGetWindowFunc(WindowObject winobj);
+
 #endif							/* WINDOWAPI_H */
-- 
2.25.1