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array_cat null reasoning

From: Kev <kevinjamesfield(at)gmail(dot)com>
To: pgsql-general(at)postgresql(dot)org
Subject: array_cat null reasoning
Date: 2008-10-27 18:08:35
Message-ID: edc50847-3caa-419f-a0c1-d7e35a90f26f@75g2000hso.googlegroups.com (view raw or flat)
Thread:
Lists: pgsql-general
Hi,

I'm a bit confused as to the logic of nulls.  I understand that null
is to represent an unknown value.  So it makes sense that the result
of tacking an unknown value onto a known one is unknown, because you
don't know what exactly you just tacked on.  So


   select null::text || 'hello';


...returning NULL makes sense.  But then why doesn't


   select array_cat(null::integer[], '{3}'::integer[]);


...also return null?  Somehow it's known what the result is when
combining an unknown array with a known one, but not when combining an
unknown text with a known one?  Doesn't this seem inconsistent?  If it
does seem inconsistent, should I be careful how to code because this
might change in the future?

Thanks,
Kev

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