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Re: subselect prob in view

From: Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com>
To: Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk>
Cc: pgsql-sql(at)postgresql(dot)org
Subject: Re: subselect prob in view
Date: 2004-06-22 13:31:22
Message-ID: 20040622062603.U13933@megazone.bigpanda.com (view raw or flat)
Thread:
Lists: pgsql-sql
On Tue, 22 Jun 2004, Gary Stainburn wrote:

> On Monday 21 Jun 2004 4:11 pm, Gary Stainburn wrote:
> > On Monday 21 Jun 2004 3:19 pm, Tom Lane wrote:
> > > Gary Stainburn <gary(dot)stainburn(at)ringways(dot)co(dot)uk> writes:
> > > >      from requests r, users u, request_types t,
> > > >           request_states s, dealerships d, departments de, customers c
> > > >           left outer join (select co_r_id, count(co_r_id) from comments
> > > > group by co_r_id) co on
> > > >             co.co_r_id = r.r_id
> > > > psql:goole1.sql:45: ERROR:  Relation "r" does not exist
> > >
> > > I think you have learned some bad habits from MySQL :-(
> > >
> > > PostgreSQL follows the SQL spec and makes JOIN bind more tightly than
> > > comma.  Therefore, in the above the LEFT JOIN is only joining "c" to
> > > "co" and its JOIN ON clause can only reference those two relations.
> > >
> > > You could get the behavior you seem to expect by changing each comma
> > > in the from-list to CROSS JOIN.  Then the JOINs all bind left-to-right
> > > and so "r" will be part of the left argument of the LEFT JOIN.
> > >
> > > Note that if you are using a pre-7.4 release this could have negative
> > > effects on performance --- see the user's guide concerning how explicit
> > > JOIN syntax constrains the planner.
> > >
> > > 			regards, tom lane
> >
> > Thanks for this Tom, but I've never used MySQL.
> >
> > I'll look at the docs and have another go.
> >
> In order to simplify things, I'm just concentrating on the view to give me the
> two tallies.  The two selects work seperately, but I'm still getting the
> syntax for the combined quiery wrong.  I'm asuming that the problem's before
> the 'on' clause and not the clause itself (I've also tried using 'using'
> instead but that didn't work either.
>
> goole=# select co.co_r_id, co.count as com_count, cor.count as com_unseen
> goole-#   from
> goole-#   (select co_r_id, count(co_r_id)
> goole(#      from comments group by co_r_id) co,
> goole-#   (select co_r_id, count(co_r_id)
> goole(#      from comments where co_id in
> goole(#      (select distinct co_id
> goole(#         from comments c, co_recipients co
> goole(#         where c.co_id = co.cor_co_id and co.cor_viewed is null)
> goole(#      group by co_r_id) cor on co.co_r_id = cor.co_r_id;

AFAICS, you're not using the join syntax between co and cor at the outer
level.  There's nothing to attach that on clause to.  Either you want that
in a where clause (like in the subselect above it) or you want to use
"inner join" between co and cor.

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Subject: Re: subselect prob in view
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