Re: Add RESPECT/IGNORE NULLS and FROM FIRST/LAST options

From: Tatsuo Ishii <ishii(at)postgresql(dot)org>
To: tgl(at)sss(dot)pgh(dot)pa(dot)us
Cc: alvherre(at)kurilemu(dot)de, ojford(at)gmail(dot)com, peter(at)eisentraut(dot)org, li(dot)evan(dot)chao(at)gmail(dot)com, krasiyan(at)gmail(dot)com, vik(at)postgresfriends(dot)org, andrew(at)tao11(dot)riddles(dot)org(dot)uk, david(at)fetter(dot)org, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: Add RESPECT/IGNORE NULLS and FROM FIRST/LAST options
Date: 2025-10-06 00:09:01
Message-ID: 20251006.090901.2288040209954599522.ishii@postgresql.org
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> will be exited this time. But there's another thing that is
> confusing: the NN_NULL case certainly looks like it's expecting
> to exit the loop, but that "break" will only get out of the switch
> not the loop.

You mean "NN_NOTNULL" case? if (notnull_offset >= notnull_relpos),
then following "while (notnull_offset < notnull_relpos)" does not
satisfy the continuous condition of the while loop and exits the loop.
I can add "goto" to explicitly exit the loop if we want.

> Moreover, the NN_NULL case looks like it'd fail
> to notice end-of-frame. And it's not entirely clear what the
> default case thinks it's doing either.

WinGetFuncArgInPartition() does not care about frame, no?

> In short, this loop is impossible to understand, and the lack of
> comments doesn't help. Even if it's not actually buggy, it
> needs to be rewritten in a way that helps readers and compilers
> see that it's not buggy. I think it might help to separate the
> detection of null-ness and fetching of the datum value (if required)
> from the loop control logic.

Thanks for the idea. Let me think if I could change the loop to be
easier to understand.

Best regards,
--
Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp

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