Re: Questionable coding in nth_value

> On Sat, May 6, 2023 at 4:44 PM Tatsuo Ishii <ishii@sraoss.co.jp> wrote:
> 
>> Currently Window function nth_value is coded as following:
>>
>>         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,
>>                 :
>>                 :
>>
>> Is there any reason why argument 'nth' is not checked earlier?
>> IMO, it is more natural "if (nth <= 0)..." is placed right after "nth =
>> DatumGetInt32...".
>>
>> Attached is the patch which does this.
> 
> 
> 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.

That makes sense. I thought since this function is marked as strict,
it would not be called if argument is NULL, but I was wrong.

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
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