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Date: Tue, 28 Aug 2007 16:35:29 +0100
From: "Sebastian Ritter" <ritter.sebastian@gmail.com>
To: pgsql-sql@postgresql.org
Subject: Re: Database normalization
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Thanks guys,

Sebastian

On 8/28/07, Bart Degryse <Bart.Degryse@indicator.be> wrote:
>
>  <quote>Im using Django as my Object relational Mapper so im pretty sure I
> can not add a constraint such as ...</quote>
> Then you should seriously consider changing your mapper.
>
> >>> "Sebastian Ritter" <ritter.sebastian@gmail.com> 2007-08-28 16:37 >>>
> Thanks for the information.
>
> Both tables would be exactly sames apart from the  foreign key relation to
> clients or services. I agree that it seems strange to have one column that
> is always null. Im using Django as my Object relational Mapper so im pretty
> sure I can not add a constraint such as : CHECK constraint where !(col1
> IS NULL and col2 IS NULL).
>
> Another factor ive been considering is that one of the fields in this
> table(s) definition(s) is free flowing text which could potentially become
> very large. Should I take this in to
> consideration when deciding whether to split the tables? In terms of
> searching speed that is.
>
> Kindest regards.
> Sebastian
>
> On 8/28/07, Andrew Sullivan <ajs@crankycanuck.ca> wrote:
> >
> > On Tue, Aug 28, 2007 at 12:47:45PM +0100, Sebastian Ritter wrote:
> > > > The update/message format is exactly the same for both. Should I
> > make two
> > > > different tables:
> >
> > > >   one table with extra columns : is_client, client_id, service_id,
> > where
> > > > either client_id or service_id would be null depending on the
> > is_client
> > > > boolean?
> >
> > Is the rest of the data the same?  If so, then one table is right.
> > If not, then more than one table.  In either case, I really hate the
> > idea of two columns, one of which is always null.  But if you're
> > going to do that, make sure you add a CHECK constraint where !(col1
> > IS NULL and col2 IS NULL).
> >
> > A
> >
> > --
> > Andrew Sullivan  | ajs@crankycanuck.ca
> > I remember when computers were frustrating because they *did* exactly
> > what
> > you told them to.  That actually seems sort of quaint now.
> >                 --J.D. Baldwin
> >
> > ---------------------------(end of broadcast)---------------------------
> > TIP 3: Have you checked our extensive FAQ?
> >
> >                http://www.postgresql.org/docs/faq
> >
>
>

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Thanks guys,<br><br>Sebastian<br><br><div><span class="gmail_quote">On 8/28/07, <b class="gmail_sendername">Bart Degryse</b> &lt;<a href="mailto:Bart.Degryse@indicator.be">Bart.Degryse@indicator.be</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">



<div style="margin: 4px 4px 1px; font-family: Tahoma; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">
<div>&lt;quote&gt;Im using Django as my Object relational Mapper so im pretty sure I can not add a constraint such as ...&lt;/quote&gt;</div>
<div>Then you should seriously consider changing your mapper.<br><br>&gt;&gt;&gt; &quot;Sebastian Ritter&quot; &lt;<a href="mailto:ritter.sebastian@gmail.com" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
ritter.sebastian@gmail.com</a>&gt; 2007-08-28 16:37 &gt;&gt;&gt;<div><span class="q" id="q_114ad121ea98d5ce_1"><br>Thanks for the information.<br><br>Both tables would be exactly sames apart from the&nbsp; foreign key relation to clients or services. I agree that it seems strange to have one column that is always null. Im using Django as my Object relational Mapper so im pretty sure I can not add a constraint such as : CHECK constraint where !(col1 
<br>IS NULL and col2 IS NULL).<br><br>Another factor ive been considering is that one of the fields in this table(s) definition(s) is free flowing text which could potentially become very large. Should I take this in to <br>
consideration when deciding whether to split the tables? In terms of searching speed that is.<br><br>Kindest regards.<br>Sebastian<br><br></span></div></div><div><span class="e" id="q_114ad121ea98d5ce_3">
<div><span class="gmail_quote">On 8/28/07, <b class="gmail_sendername">Andrew Sullivan </b>&lt;<a href="mailto:ajs@crankycanuck.ca" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">ajs@crankycanuck.ca
</a>&gt; wrote:</span>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">On Tue, Aug 28, 2007 at 12:47:45PM +0100, Sebastian Ritter wrote: <br>&gt; &gt; The update/message format is exactly the same for both. Should I make two
<br>&gt; &gt; different tables:<br><br>&gt; &gt;&nbsp;&nbsp; one table with extra columns : is_client, client_id, service_id, where<br>&gt; &gt; either client_id or service_id would be null depending on the is_client <br>&gt; &gt; boolean?
<br><br>Is the rest of the data the same?&nbsp;&nbsp;If so, then one table is right.<br>If not, then more than one table.&nbsp;&nbsp;In either case, I really hate the<br>idea of two columns, one of which is always null.&nbsp;&nbsp;But if you&#39;re <br>
going to do that, make sure you add a CHECK constraint where !(col1<br>IS NULL and col2 IS NULL).<br><br>A<br><br>--<br>Andrew Sullivan&nbsp;&nbsp;| <a href="mailto:ajs@crankycanuck.ca" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">
ajs@crankycanuck.ca</a><br>I remember when computers were frustrating because they *did* exactly what <br>you told them to.&nbsp;&nbsp;That actually seems sort of quaint now.<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;--J.D. Baldwin<br><br>---------------------------(end of broadcast)---------------------------
<br>TIP 3: Have you checked our extensive FAQ? <br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a href="http://www.postgresql.org/docs/faq" target="_blank" onclick="return top.js.OpenExtLink(window,event,this)">http://www.postgresql.org/docs/faq</a>
<br></blockquote></div><br></span></div></div>
</blockquote></div><br>

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