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

From: Rikard Pavelic <rikard(dot)pavelic(at)zg(dot)htnet(dot)hr>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: BUG #6701: IS NOT NULL doesn't work on complex composites
Date: 2012-06-21 00:16:23
Message-ID: 4FE267D7.9080202@zg.htnet.hr (view raw or flat)
Thread:
Lists: pgsql-bugs
On 20.6.2012. 21:10, Tom Lane wrote:
> rikard(dot)pavelic(at)zg(dot)htnet(dot)hr writes:
>> create type t AS (i int); create type complex as (t t, i int); create table bad(i int, c complex); --This doesn't work as expected select * from bad where c is not null; 
> What do you consider to be "expected"? Have you read the documentation where it points out that IS NULL and IS NOT NULL are not inverses for composite values?
> http://www.postgresql.org/docs/9.1/static/functions-comparison.html (I'm not that thrilled with this behavior either, but it is per SQL standard AFAICT.) regards, tom lane

I understand the concept behind if one composite property is null then then IS NULL check returns NULL (instead true or false).
I can even understand IS NULL check returning false.

I can use ::text to get what I expected,
but Postgres still seems inconsistent in handling NULL checks.

create type complex as (i int, j int);
create table t (i int, c complex not null);

--error as expected
insert into t values(1, null);

--unexpected - passed!?
insert into t values(1, (null,4));

-- this is false - I think it would be better if it's null, but lets move on
select (null, 4) is not null

--lets try again with check constraint
alter table t add check(c is not null);

--error as expected from is not null check above
insert into t values(1, (null,4));

It seems that check constraint behaves differently.
Docs say: (http://www.postgresql.org/docs/9.1/static/ddl-constraints.html)
"A not-null constraint is functionally equivalent to creating a check constraint CHECK (column_name IS NOT NULL)"
And at least there is more notes required ;(

Let's try some more.

create table x (i int, c complex);

insert into x values(1,null);
insert into x values(2,(1,null));
insert into x values(3,(1,2));

--first row - ok
select * from x where c is null;

--last row - ok
select * from x where c is not null;

--unexpected result again
select c is null from x;

I must admit I was expecting
true
null
false

Regards,
Rikard

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