Re: Questionable coding in nth_value

Hmm, shouldn't we check if the argument of nth_value is null before we
check if it is greater than zero?  So maybe we need to do this.

--- a/src/backend/utils/adt/windowfuncs.c
+++ b/src/backend/utils/adt/windowfuncs.c
@@ -698,13 +698,14 @@ window_nth_value(PG_FUNCTION_ARGS)
    nth = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
    if (isnull)
        PG_RETURN_NULL();
-   const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);

    if (nth <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_ARGUMENT_FOR_NTH_VALUE),
                 errmsg("argument of nth_value must be greater than zero")));

+   const_offset = get_fn_expr_arg_stable(fcinfo->flinfo, 1);
+
    result = WinGetFuncArgInFrame(winobj, 0,
                                  nth - 1, WINDOW_SEEK_HEAD, const_offset,
                                  &isnull, NULL);

Thanks
Richard