Message-ID: <59fe567f-ba41-4cc2-b04a-a830288ea929@postgresfriends.org>
Date: Tue, 18 Nov 2025 12:19:46 +0100
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Subject: Re: Row pattern recognition
To: Chao Li <li.evan.chao@gmail.com>, Tatsuo Ishii <ishii@postgresql.org>
Cc: david.g.johnston@gmail.com, jacob.champion@enterprisedb.com,
 er@xs4all.nl, peter@eisentraut.org, pgsql-hackers@postgresql.org
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 <DBA30B4B-F611-46AC-807D-027D3CBEDEC9@gmail.com>
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From: Vik Fearing <vik@postgresfriends.org>
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On 18/11/2025 06:03, Chao Li wrote:
> 1 - 0001 - kwlist.h
> ```
> +PG_KEYWORD("define", DEFINE, RESERVED_KEYWORD, BARE_LABEL)
> ```
>
> Why do we add “define” as a reserved keyword? From the SQL example you put in 0006:
> ```
> <programlisting>
> SELECT company, tdate, price,
>   first_value(price) OVER w,
>   max(price) OVER w,
>   count(price) OVER w
> FROM stock
>   WINDOW w AS (
>   PARTITION BY company
>   ORDER BY tdate
>   ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
>   AFTER MATCH SKIP PAST LAST ROW
>   INITIAL
>   PATTERN (LOWPRICE UP+ DOWN+)
>   DEFINE
>    LOWPRICE AS price &lt;= 100,
>    UP AS price &gt; PREV(price),
>    DOWN AS price &lt; PREV(price)
> );
> </programlisting>
> ```
>
> PARTITION is at the same level as DEFINE, but it’s not defined as a reserved keyword:
> ```
> PG_KEYWORD("partition", PARTITION, UNRESERVED_KEYWORD, BARE_LABEL)
> ```
>
> Even in this patch,”initial”,”past”, “pattern” and “seek” are defined as unreserved, why?
>
> So I just want to clarify.


Because of position. Without making DEFINE a reserved keyword, how do 
you know that it isn't another variable in the PATTERN clause?

-- 

Vik Fearing