Skip site navigation (1) Skip section navigation (2)

Re: Pet Peeves?

From: Octavio Alvarez <alvarezp(at)alvarezp(dot)ods(dot)org>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: Pet Peeves?
Date: 2009-01-31 23:54:10
Message-ID: 1233446050.5647.73.camel@localhost.localdomain (view raw or flat)
Thread:
Lists: pgsql-general
On Sat, 2009-01-31 at 23:36 +0000, Gregory Stark wrote:
> Octavio Alvarez <alvarezp(at)alvarezp(dot)ods(dot)org> writes:
> 
> > A crosstab is not but a presentational transform of the data set. Any
> > information you would eventually need can be taken from the original
> > data source, one way or another. That's why dynamic-column crosstab are
> > not a problem, and the DBMS should not worry about providing the
> > information about the columns, maybe by simply not allowing the
> > dynamic-column ones in subqueries.
> 
> What about a WHERE clause like
> 
> WHERE P1 > P2

You could either:

(1) do "FROM grades AS g1 INNER JOIN grades AS g2 ON g1.P1 > g2.P2",
generating the record set before applying the crosstab transformation.

(2) Since you are implying the existence of P1 and P2, use the
fixed-number-of-columns crosstab case instead, for which PG would
actually be able to give the column definitions without running the
query, and after that, joining the results with some other query.


In response to

Responses

pgsql-general by date

Next:From: Kevin MurphyDate: 2009-02-01 00:52:31
Subject: Re: Indices types, what to use. Btree, Hash, Gin or Gist
Previous:From: Cliff PrattDate: 2009-01-31 23:47:53
Subject: Re: [GENERAL] Encoding problem using pg_dumpall

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group