Function WinGetFuncArgInPartition

src/backend/executor/nodeWindowAgg.c:3586–3639

* WinGetFuncArgInPartition * Evaluate a window function's argument expression on a specified * row of the partition. The row is identified in lseek(2) style, * i.e. relative to the current, first, or last row. * * argno: argument number to evaluate (counted from 0) * relpos: signed rowcount offset from the seek position * seektype: WINDOW_SEEK_CURRENT, WINDOW_SEEK_HEAD, or WINDOW_SEEK_T

 * (plus setting *isout true, if isout isn't NULL).
 */
Datum
WinGetFuncArgInPartition(WindowObject winobj, int argno,
						 int relpos, int seektype, bool set_mark,
						 bool *isnull, bool *isout)
{
	WindowAggState *winstate;
	ExprContext *econtext;
	TupleTableSlot *slot;
	bool		gottuple;
	int64		abs_pos;

	Assert(WindowObjectIsValid(winobj));
	winstate = winobj->winstate;
	econtext = winstate->ss.ps.ps_ExprContext;
	slot = winstate->temp_slot_1;

	switch (seektype)
	{
		case WINDOW_SEEK_CURRENT:
			abs_pos = winstate->currentpos + relpos;
			break;
		case WINDOW_SEEK_HEAD:
			abs_pos = relpos;
			break;
		case WINDOW_SEEK_TAIL:
			spool_tuples(winstate, -1);
			abs_pos = winstate->spooled_rows - 1 + relpos;
			break;
		default:
			elog(ERROR, "unrecognized window seek type: %d", seektype);
			abs_pos = 0;		/* keep compiler quiet */
			break;
	}

	gottuple = window_gettupleslot(winobj, abs_pos, slot);

	if (!gottuple)
	{
		if (isout)
			*isout = true;
		*isnull = true;
		return (Datum) 0;
	}
	else
	{
		if (isout)
			*isout = false;
		if (set_mark)
			WinSetMarkPosition(winobj, abs_pos);
		econtext->ecxt_outertuple = slot;
		return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
							econtext, isnull);
	}
}

/*
 * WinGetFuncArgInFrame