Re: SQL/MED - core functionality

On Wed, Dec 22, 2010 at 03:00:16PM +0000, Simon Riggs wrote:
> On Wed, 2010-12-22 at 09:03 -0500, Andrew Dunstan wrote:
> 
> > Answering a few of your questions
> 
> Many thanks.
> 
> > > 7. Why does ANALYZE skip foreign tables? Surely its really
> > > important we know things about a foreign table, otherwise we are
> > > going to optimize things very badly.
> > 
> > Quite apart from other reasons, such as possible ephemerality of
> > the data, the difficulty of taking a reasonable random sample from
> > an arbitrary foreign data source seems substantial, and we surely
> > don't want ANALYSE to have to run a full sequential scan of a
> > foreign data source.
> 
> I think we need something that estimates the size of a table, at
> least, otherwise queries will be completely un-optimised.

The estimated size for a lot of things--streams of data, for
example--is infinity.  I suppose that's a good default for some cases.

> > > 10. Can a foreign table be referenced by a FK?
> > 
> > I don't see how it can be. There would be no unique index to use.
> 
> That answers another question also.

There might be some cases where we can say an expression on a set of
columns is unique, but not in the general case.  In the general case,
we can't even guarantee 1NF.

> Still many unanswered.

Will try these later today :)

Cheers,
David.
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