From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Kevin Grittner <kgrittn(at)ymail(dot)com> |
Cc: | Peter Geoghegan <pg(at)heroku(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>, Craig Ringer <craig(at)2ndquadrant(dot)com> |
Subject: | Re: INSERT ... ON CONFLICT {UPDATE | IGNORE} |
Date: | 2014-09-29 22:02:23 |
Message-ID: | 20140929220223.GI2084@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-09-29 14:57:45 -0700, Kevin Grittner wrote:
> Peter Geoghegan <pg(at)heroku(dot)com> wrote:
>
> > I think the fact that no MERGE implementation does what you want
> > should be convincing. It is *horrifically* complicated to make
> > what you want work, if indeed it is technically feasible at all.
> > Isn't this already complicated enough?
>
> What about the MERGE syntax I posted makes it hard to implement the
> statement validation and execution code you already have? (I'm
> asking about for the UPSERT case only, not an implementation of all
> aspects of the standard syntax.)
> To recap, in summary that would be:
>
> MERGE INTO tablename [ alias ]
> USING ( relation ) [ alias ]
> ON ( boolean-expression )
> WHEN MATCHED THEN
> UPDATE SET target-column = expression
> [ , target-column = expression ] ...
> WHEN NOT MATCHED THEN
> INSERT ( target-columns ) VALUES ( expressions )
>
> The initial implementation could restrict to these exact clauses
> and require that the boolean-expression used equality-quals on all
> columns of a unique index on only NOT NULL columns.
That'll make it really hard to actually implement real MERGE.
Because suddenly there's no way for the user to know whether he's
written a ON condition that can implement UPSERT like properties
(i.e. the *precise* column list of an index) or not.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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