I'm a little concerned about stability since my Postgresql application has
failed three times in the last couple of months. It seems to have failed
when too many things are happening at the same time - mostly things that
have been instigated by my pointing and clicking.
Bob
----- Original Message -----
From: "Michael Glaesemann" <grzm@xxxxxxxxxxxxx>
To: "Bob Pawley" <rjpawley@xxxxxxx>
Cc: "Postgresql" <pgsql-general@xxxxxxxxxxxxxx>
Sent: Tuesday, January 31, 2006 5:18 PM
Subject: Re: [GENERAL] Data Conversion
On Feb 1, 2006, at 9:53 , Bob Pawley wrote:
Two way conversion will be a neccesity. My thought was that dual
conversion could be not only complex but also have problems with
stability.
I'm not sure why it would be a stability issue. As for the complexity, I
think once it's implemented you wouldn't have to worry about it by
properly encapsulating that complexity, perhaps in procedures. I guess
one way to handle the dual conversion issue is to produce a view (based
on my previous example)
create view measurement_conversions_view as
select measurement_type
, measurement_unit_in
, measurement_unit_out
, factor
from measurement_conversions
union
select measurement_type
, measurement_unit_out as measurement_unit_in
, measurement_unit_in as measurement_unit_out
, 1::numeric / factor as factor
from measurement_conversions
union
select measurement_type
, measurement_unit as measurement_unit_in
, measurement_unit as measurement_unit_out
, 1 as factor
from measurement_units
It'd also be good to add a constraint (through a trigger) that guarantees
that if, for example, the length conversion m => in is the
measurement_conversions table, the conversion in => m can't be inserted.
This would prevent duplicates in the measurement_conversions_view (and
corresponding possible errors arising from slightly different conversion
results).
Option 2 would be less complex and there would be less potential
stability problems. However, there is some perception of redundancy in
having two or more tables contain similar information. But, is it only a
perception???
It's not just a perception. You're duplicating the values. You need to
always make sure that you're inserting into, updating, and deleting from
all of the relevant tables. I think that would be a maintenance
nightmare.
Michael Glaesemann
grzm myrealbox com
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