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Re: BUG #6701: IS NOT NULL doesn't work on complex composites

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com>, <pgsql-bugs(at)postgresql(dot)org>, "Rikard Pavelic" <rikard(dot)pavelic(at)zg(dot)htnet(dot)hr>
Subject: Re: BUG #6701: IS NOT NULL doesn't work on complex composites
Date: 2012-06-21 17:43:18
Message-ID: 4FE316E602000025000488B1@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-bugs
Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
 
>> So currently a NOT NULL constraint on a column with a composite
>> type is equivalent to:
>> CHECK (NOT c IS NULL)
> 
> I don't believe this statement is accurate.  What's really
> happening is that a column-not-null constraint is a
> datatype-independent check for whether the datum per se is null or
> not.
 
I stand corrected.
 
> Somebody who really cares about having the SQL-spec definition can
> write a CHECK constraint as suggested above, and then he'll get
> the composite-type-aware behavior, so it's not like there's no way
> to get that.
> 
> BTW, the same inconsistency exists for function-argument
> strictness checks: those will consider a heaptuple-of-all-nulls to
> be something you can call a strict function with.  I think
> changing this would be a pretty bad idea, not only on modularity
> and performance grounds but because it'd likely break existing
> applications that expect the current behavior.
 
Maybe a comment or two in the docs covers it?
 
> regression=# select null::int8_tbl is distinct from 
> row(null,null)::int8_tbl;
>  ?column? 
> ----------
>  t
> (1 row)
> 
> It's not clear to me whether the SQL standard rules on what should
> happen in this case, or whether we should listen to it if it does
> say that these values are not distinct.  They certainly *look*
> distinct.
 
I do sympathize with the point of view that a row value about which
absolutely no applicable facts are known is a lot like not knowing
what row you have, but they do seem distinct when you look at the
output.
 
> (Oh, and dare I mention arrays of nulls?)
 
Hey, look!  An elephant!
 
-Kevin

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Next:From: Tom LaneDate: 2012-06-21 18:23:52
Subject: Re: BUG #6701: IS NOT NULL doesn't work on complex composites
Previous:From: Feng GaoDate: 2012-06-21 17:39:43
Subject: Bug #6201 status.

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