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Message-ID: <441566CF.2040105@logix-tt.com>
Date: Mon, 13 Mar 2006 13:34:23 +0100
From: Markus Schaber <schabi@logix-tt.com>
Organization: Logical Tracking and Tracing International AG, Switzerland
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To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: PostgreSQL SQL List <pgsql-sql@postgresql.org>
Subject: Re: Set generating functions and subqueries
References: <44116ED2.9060901@logix-tt.com> <5142.1142002128@sss.pgh.pa.us>
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Hi, Tom,

Tom Lane wrote:

> The behavior of the subquery expression is dictated by the SQL spec:
> 
>          1) If the cardinality of a <scalar subquery> or a <row subquery> is
>             greater than 1, then an exception condition is raised: cardinal-
>             ity violation.

That's interesting to know, and it seems to be a clean design.

> The fact that the other form is even allowed is more of a holdover from
> PostQUEL than something we have consciously decided is a good idea.
> (IMHO it's actually a fairly *bad* idea, because it does not work nicely
> when there's more than one SRF in the same targetlist.)  It'll probably
> get phased out someday, if we can find a way to replace the
> functionality.  I seem to recall speculating that SQL2003's LATERAL
> tables might do the job.

AFAICS, it can be replaced with JOINs:

select * FROM (SELECT 'othercol' AS other) as foo CROSS JOIN (SELECT
generate_series(1,2) as a) as fop CROSS JOIN (SELECT
generate_series(3,4) as b) AS foq;
  other   | a | b
----------+---+---
 othercol | 1 | 3
 othercol | 2 | 3
 othercol | 1 | 4
 othercol | 2 | 4
(4 rows)

> No kidding.

I wasn't kidding, I just wanted to point out the different behaviour
between equal-length and inequal-length sequences.


Thanks,
markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

Fight against software patents in EU! www.ffii.org www.nosoftwarepatents.org