Horton

Re: support for MERGE

Justin Pryzby <pryzby@telsasoft.com>

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From: Justin Pryzby <pryzby@telsasoft.com>
To: Álvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Peter Eisentraut <peter.eisentraut@enterprisedb.com>, Amit Langote <amitlangote09@gmail.com>, Japin Li <japinli@hotmail.com>, Zhihong Yu <zyu@yugabyte.com>, Simon Riggs <simon.riggs@enterprisedb.com>, pgsql-hackers@lists.postgresql.org, Tomas Vondra <tomas.vondra@enterprisedb.com>, Daniel Westermann <dwe@dbi-services.com>, Erik Rijkers <er@xs4all.nl>, Jaime Casanova <jcasanov@systemguards.com.ec>, Andres Freund <andres@anarazel.de>
Date: 2022-08-01T14:52:57Z
Lists: pgsql-hackers 
On Tue, Jun 14, 2022 at 11:27:06AM +0200, Álvaro Herrera wrote:
> @@ -448,9 +448,9 @@ COMMIT;
>      and execute the first one that succeeds.
>      If <command>MERGE</command> attempts an <command>INSERT</command>
>      and a unique index is present and a duplicate row is concurrently
> -    inserted, then a uniqueness violation is raised.
> -    <command>MERGE</command> does not attempt to avoid the
> -    error by executing an <command>UPDATE</command>.
> +    inserted, then a uniqueness violation error is raised;
> +    <command>MERGE</command> does not attempt to avoid such
> +    errors by evaluating <literal>MATCHED</literal> conditions.

This was a portion of a chang that was committed as ffffeebf2.

But I don't understand why this changed from "does not attempt to avoid the
error by executing an <command>UPDATE</command>." to "...by evaluating
<literal>MATCHED</literal> conditions."

Maybe it means to say "..by re-starting evaluation of match conditions".

Sorry to re-raise this 6 weeks later..

-- 
Justin

Commits

  1. Doc fixes for MERGE statement

  2. MERGE docs adjustments

  3. Link to MVCC docs in MERGE docs

  4. Fix EXPLAIN MERGE output when no tuples are processed

  5. Make EXPLAIN MERGE output format more compact

  6. Add support for MERGE SQL command

  7. Split ExecUpdate and ExecDelete into reusable pieces

  8. Add API of sorts for transition table handling in trigger.c

  9. Represent Lists as expansible arrays, not chains of cons-cells.