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Re: Row pattern recognition

Tatsuo Ishii <ishii@postgresql.org>

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From: Tatsuo Ishii <ishii@postgresql.org>
To: ssam258@gmail.com
Cc: vik@postgresfriends.org, er@xs4all.nl, jacob.champion@enterprisedb.com, david.g.johnston@gmail.com, peter@eisentraut.org, pgsql-hackers@postgresql.org
Date: 2026-02-12T01:17:01Z
Lists: pgsql-hackers 
Hi Henson,

I found following in rpr_base.sql:

-- {0} is not allowed (min must be >= 1)
SELECT id, val, COUNT(*) OVER w as cnt
FROM rpr_quant
WINDOW w AS (
    ORDER BY id
    ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
    PATTERN (A{0} B)
    DEFINE A AS val > 1000, B AS val > 0
)
ORDER BY id;

However in my uderstanding the SQL standard allows A{0}.

PATTERN (A{0} B)
is equivalant to:
PATTERN (B)

Another interesting PATTERN is:

A{,}

This is equivalant to A{0,}

BTW, after studied this more, I found that A{0,0} is not allowed. In
this form the right hand side number shall be greater than 0. From
ISO/IEC 9075-2 7.9 <row pattern syntax> "Syntax Rules 20)

"If <left brace> <unsigned integer> <comma> <unsigned integer> <right
brace> is specified, then let VUI1 and VUI2 be the values of the first
and second <unsigned integer>'s, respectively. VUI1 shall be less than
or equal to VUI2, and VUI2 shall be greater than 0 (zero)."

However according to the Google, Oracle and Snowflake allows A{0,0}:
they break the standard. So, what do you think PostgreSQL should do
here?  My preference is "always follow the standard". But others might
think differently.

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

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Adjust cross-version upgrade tests for seg_out() fix

  2. Rationalize error comments in partition split/merge tests

  3. Add fast path for foreign key constraint checks

  4. Fix assorted pretty-trivial memory leaks in the backend.

  5. Add temporal FOREIGN KEY contraints

  6. Add trailing commas to enum definitions

  7. Remove obsolete executor cleanup code