| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
| Cc: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Peter Geoghegan <pg(at)bowt(dot)ie>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>, Andrew Dunstan <andrew(dot)dunstan(at)2ndquadrant(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)2ndquadrant(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] MERGE SQL Statement for PG11 |
| Date: | 2018-02-06 03:49:29 |
| Message-ID: | CA+Tgmoa_QaaDUVHMFpYoM1sLNMOYp4KMXvvWJm69axx39Do9NA@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Sun, Feb 4, 2018 at 3:41 AM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
>> It is not clear to me what is exactly your concern if we try to follow
>> #2? To me, #2 seems like a natural choice.
>
> At first, but it gives an anomaly so is not a good choice. The patch
> does behavior #5, it rechecks the conditions with the latest row.
>
> Otherwise
> WHEN MATCHED AND a=0 THEN UPDATE SET b=0
> WHEN MATCHED AND a=1 THEN UPDATE SET b=1
> would result in (a=1, b=0) in case of concurrent updates, which the
> user clearly doesn't want.
I am unable to understand this. What are you presuming the tuple was
originally?
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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