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

> Thank you for the patch. (I noticed int8 is also missing).
> 
> I have looked into the commit 964d01ae90c3 which was made by Peter.  I
> have quick read through the discussion to know why uint8/uint16 (and
> int8) are missing in gen_node_support.pl. Unfortunately I have no
> clear idea why these data types are missing in the script.
> 
> Peter,
> Maybe you wanted to limit the data types that are actually used at
> that point? If so, probably we should only add uint8 support this time
> (uint8 is only needed to implement $Subject for now).  What do you
> think?

I decided not to include the fix to gen_node_support.pl for now and
commit the patch without it. We could revisit it later on.

So here is the commit message I would like to propose.

For the technical part please look at the message.

Non technical part:
First of all the author is Oliver (no doubt).  I would like to be
listed as a co-author since I wrote the not null cache part.

Next is reviewers. Actually the first effor to implement null
treatment clause was back to 9.3 era (2013) at least. After that
multiple trials to implemnt the feature happend but they had faded
away. I think we don't need to include all of those who joined the old
discussions as reviewers. So I started to check from the discussion:
https://postgr.es/m/flat/CAGMVOdsbtRwE_4+v8zjH1d9xfovDeQAGLkP_B6k69_VoFEgX-A@mail.gmail.com
because it's refered to by the commit fest entry.

Oliver and others, I love to hear your comment!

BTW, Oliver's last patch made the CF bot to misunderstand the patch
contents, which was not actually the main patch. So I attach the same
patch as v20.

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Add IGNORE NULLS/RESPECT NULLS option to Window functions.

Add IGNORE NULLS/RESPECT NULLS option (null treatment clause) to lead,
lag, first_value, last_value and nth_value window functions.  If
unspecified, the default is RESPECT NULLS which includes NULL values
in any result calculation. IGNORE NULLS ignores NULL values.

Built-in window functions are modified to call new API
WinCheckAndInitializeNullTreatment() to indicate whether they accept
IGNORE NULLS/RESPECT NULLS option or not (the API can be called by
user defined window functions as well).  If WinGetFuncArgInPartition's
allowNullTreatment argument is true and IGNORE NULLS option is given,
WinGetFuncArgInPartition() or WinGetFuncArgInFrame() will return
evaluated function's argument expression on specified non NULL row (if
it exists) in the partition or the frame.

When IGNORE NULLS option is given, window functions need to visit and
evaluate same rows over and over again to look for non null rows. To
mitigate the issue, 2-bit not null information array is created while
executing window functions to remember whether the row has been
already evaluated to NULL or NOT NULL. If already evaluated, we could
skip some the evaluation work, thus we could get better performance.

Author: Oliver Ford <ojford@gmail.com>
Co-authored-by: Tatsuo Ishii <ishii@postgresql.org>
Reviewed-by: Andrew Gierth <andrew@tao11.riddles.org.uk>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: David Fetter <david@fetter.org>
Reviewed-by: Vik Fearing <vik@postgresfriends.org>
Reviewed-by: "David G. Johnston" <david.g.johnston@gmail.com>
Reviewed-by: Krasiyan Andreev <krasiyan@gmail.com>
Reviewed-by: Chao Li <lic@highgo.com>
Discussion: https://postgr.es/m/flat/CAGMVOdsbtRwE_4+v8zjH1d9xfovDeQAGLkP_B6k69_VoFEgX-A@mail.gmail.com
----------------------------------------------------------------------

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