Re: SELECT INSTEAD - Mailing list pgsql-sql

Thanks Michael - The 2 queries (sorry, should have said transaction) are a
simple way to identify duplicates in our mailing list. If there are
triplicates, the first query will return 6 rows into the temp table, 1 for
each of the 2 duplicates), but I only need to show the 3 triplicates once
each, not twice each. The DISTINCT ON does that, and that's basically the
whole reason I need to put it in to a temp table and re-select from that,
otherwise I have to sort by the id column (ORDER BY must match DISTINCT ON
expression). Sorting by the ID column doesn't "group" the duplicate /
triplicate rows together for review - that's why I need the ORDER BY.

I guess I could remove the ORDER BY, which eliminates my need to use the
temp table and 2 queries, then do the ordering when I select the view...?

Cheers,
~p

-----Original Message-----
From: Michael Fuhr [mailto:mike@fuhr.org] 
Sent: Thursday, 29 March 2007 16:49
To: Phillip Smith
Cc: pgsql-sql@postgresql.org
Subject: Re: [SQL] SELECT INSTEAD

On Thu, Mar 29, 2007 at 03:35:52PM +1000, Phillip Smith wrote:
> I'm trying to create a view of the query below, but I'm being barked at
> about "rules on SELECT must have action INSTEAD SELECT". I don't have any
> rules in my database, and I don't know how this query is trying to create
> one.

http://www.postgresql.org/docs/8.2/interactive/rules-views.html

"Views in PostgreSQL are implemented using the rule system."

> The query does work if I just run it interactively. Any help would be
> much appreciated.

You showed two queries, not one.  The error occurs because you're
trying to create a view that creates a temporary table; you'll need
to write the two queries as a single query that doesn't use a
temporary table.  Also, are you sure you need DISTINCT ON (m1.id)?
What do you intend for that to do?  Is id unique (PRIMARY KEY or
UNIQUE)?  And unless ORDER BY is necessary to determine the result
set (as with DISTINCT ON) then consider leaving it out of the view
definition -- if the outermost query (the query that selects from
the view) needs a certain order than that's the proper place for
ORDER BY.

-- 
Michael Fuhr


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