Why is NULL = unbounded for rangetypes?

From: Andreas Joseph Krogh <andreak(at)officenet(dot)no>
To: Postgres General <pgsql-general(at)postgresql(dot)org>
Subject: Why is NULL = unbounded for rangetypes?
Date: 2013-07-08 08:19:18
Message-ID: OrigoEmail.b39.9039764ca71b5d10.13fbd566210@prod2
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<div>Hi.</div>

<div> </div>

<div>Both of these queries return TRUE because NULL means &quot;unmounded&quot;:</div>

<div>
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<pre class="western" style="text-align: left">
<font face="DejaVu Sans Mono"><font color="#000080"><b>select daterange</b></font><font color="#000000">(</font><font color="#008000"><b>'2013-07-01' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#000080"><b>null</b></font><font color="#000000">, </font><font color="#008000"><b>'[]'</b></font><font color="#000000">) &amp;&amp; </font><font color="#000080"><b>daterange</b></font><font color="#000000">(</font><font color="#008000"><b>'2013-07-04' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#008000"><b>'2013-07-30' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#008000"><b>'[]'</b></font><font color="#000000">);</font></font>
<font face="DejaVu Sans Mono"><font color="#000080"><b>select daterange</b></font><font color="#000000">(</font><font color="#000080"><b>null</b></font><font color="#000000">, </font><font color="#008000"><b>'2013-08-11' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#008000"><b>'[]'</b></font><font color="#000000">) &amp;&amp; </font><font color="#000080"><b>daterange</b></font><font color="#000000">(</font><font color="#008000"><b>'2013-07-04' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#008000"><b>'2013-07-30' </b></font><font color="#000000">:: </font><font color="#000080"><b>DATE</b></font><font color="#000000">, </font><font color="#008000"><b>'[]'</b></font><font color="#000000">);</font></font></pre>

<div>What is the rational behind this behavior of NULL?</div>
</div>

<div> 
<div class="origo-email-signature">--<br>
Andreas Joseph Krogh &lt;andreak(at)officenet(dot)no&gt;      mob: +47 909 56 963<br>
Senior Software Developer / CTO - OfficeNet AS - http://www.officenet.no<br>
Public key: http://home.officenet.no/~andreak/public_key.asc</div>
</div>

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