Date: Fri, 27 Oct 2017 14:45:55 +0200
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: MERGE SQL Statement for PG11
Message-ID: <20171027124555.txawx6p6veikx25x@alvherre.pgsql>
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Simon Riggs wrote:

> Earlier thoughts on how this could/could not be done were sometimes
> imprecise or inaccurate, so I have gone through the command per
> SQL:2011 spec and produced a definitive spec in the form of an SGML
> ref page. This is what I intend to deliver for PG11.

Nice work.  I didn't verify the SQL spec, just read your HTML page;
some very minor comments based on that:

* use "and" not "where" as initial words in "when_clause" and
  "merge_update" clause definitions

* missing word here: "the DELETE privilege on the if you specify"

* I think the word "match." is leftover from some editing in the phrase
  " that specifies which rows in the data_source match rows in the
  target_table_name. match."  In the same paragraph, it is not clear
  whether all columns must be matched or it can be a partial match.

* In the when_clause note, it is not clear whether you can have multiple
  WHEN MATCHED and WHEN NOT MATCHED clauses.  Obviously you can have one
  of each, but I think your doc says it is possible to have more than one of
  each, with different conditions (WHEN MATCHED AND foo THEN bar WHEN
  MATCHED AND baz THEN qux).  No example shows more than one.

  On the same point: Is there short-circuiting of such conditions, i.e.
  will the execution will stop looking for further WHEN matches if some
  rule matches, or will it rather check all rules and raise an error if
  more than one WHEN rules match each given row?

* Your last example uses ELSE but that appears nowhere in the synopsys.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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