Date: Thu, 12 Aug 2004 07:36:37 -0700 (PDT)
From: Stephan Szabo <sszabo@megazone.bigpanda.com>
To: Philippe Lang <philippe.lang@attiksystem.ch>
Cc: pgsql-sql@postgresql.org
Subject: Re: function expression in FROM may not refer to other relations
In-Reply-To: <6C0CF58A187DA5479245E0830AF84F420803B7@poweredge.attiksystem.ch>
Message-ID: <20040812073151.G56533@megazone.bigpanda.com>
References: <6C0CF58A187DA5479245E0830AF84F420803B7@poweredge.attiksystem.ch>
MIME-Version: 1.0
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On Thu, 12 Aug 2004, Philippe Lang wrote:

> > > The problem now is that get_lines is being called twice per line.
> >
> > Is get_lines() defined as IMMUTABLE?  Should it be?
>
> I have tried defining get_lines as "IMMUTABLE", or "WITH (iscachable)",
> but it keeps on getting called twice per line in the following query...
>
> select
>   id,
>   usr,
>   code,
>   (get_lines(code)).line1,
>   (get_lines(code)).line2
> from tbl;
>
> I wish there was a way to run the query like this:
>
> select
>   id,
>   usr,
>   code,
>   CAST(get_lines(code) as lines)
> from tbl;

Note that
 select id, usr, code, get_lines(code) from tbl;
should work in 8.0beta although you get the composite type as
the last column, not two columns.

sszabo=# select id, usr, code, get_lines(code) from tbl;
 id |  usr  | code | get_lines
----+-------+------+-----------
  1 | one   |    1 | (A,B)
  2 | two   |    2 | (Z,Z)
  3 | three |    1 | (A,B)
(3 rows)

You can get individual columns with a bit of work and a subselect in from
but you need to trick the system to not pull up the subselect to not get
the function called twice per row.