Re: Overlap operators for ARRAY and NULLs

I have added a link to this from the exiting TODO item:

Improve handling of NULLs in arrays

* BUG #4509: array_cat's null behaviour is inconsistent
* http://archives.postgresql.org/pgsql-hackers/2010-11/msg01040.php

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Itagaki Takahiro wrote:
> There might be inconsistency in overlap operators for array
> types ( <@, @>, and && ) when the argument arrays contain NULLs.
>
> - SELECT 2 = ANY (ARRAY[1, NULL]) => NULL
> - SELECT ARRAY[2] <@ ARRAY[1, NULL] => false
>
> NULL means "unknown" in definition, so should it return NULL
> rather than false?
>
> I found the issue when I read spec of MULTISET. In the SQL
> standard, the following expression returns NULL. I was thinking
> to make SUBMULTISET OF to be an alias of <@ operator, but
> they seems to be incompatible.
>
> - MULTISET[2] SUBMULTISET OF MULTISET[1, NULL] => NULL
>
> Will we change the operator's behavior? It would be more
> consistent, but incompatible with older server versions.
> If impossible, I'll add separated submultiset_of() function
> instead of <@ operator for MULTISET supports.
>
> --
> Itagaki Takahiro
>
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--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +