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From "Oleksandr Alesinskyy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-2212) Add "Unique where not null" to create index
Date Wed, 07 Nov 2007 12:25:50 GMT

    [ https://issues.apache.org/jira/browse/DERBY-2212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540728
] 

Oleksandr Alesinskyy commented on DERBY-2212:
---------------------------------------------

Anurag,

There are still hordes of typos (both in the functional specification 
and your last comment). I'm really afraid that patch source would be 
done with the same level of accuracy :(

In my opinion ithe functional specification must point that for time 
beeing implementation depends on appropriate extension of the behavior 
of the unique index and refer to task of exposing of this new behavior 
to the user.

One more point - this change for sure will affect optimizer behavior and 
will require modification in it, but specification completely miss this 
point.

Regards,
Oleksandr

* "Anurag Shekhar (JIRA)" <jira@apache.org> [Wed, 7 Nov 2007 01:07:50 
https://issues.apache.org/jira/browse/DERBY-2212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12540705
version I
https://issues.apache.org/jira/browse/DERBY-2212
derby-2212preview2.diff,
(as
treat
bahavior
(both
meaning
differs
etc.).

--
Oleksandr Alesinskyy.


> Add "Unique where not null" to create index
> -------------------------------------------
>
>                 Key: DERBY-2212
>                 URL: https://issues.apache.org/jira/browse/DERBY-2212
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>    Affects Versions: 10.2.1.6
>            Reporter: Oleksandr Alesinskyy
>            Assignee: Anurag Shekhar
>         Attachments: derby-2212preview.diff, derby-2212preview2.diff, FunctionalSpec.html,
FunctionalSpecV3.html, FunctionlaSpecv2.html
>
>
> Derby prohibits creation of unique constraints on nullable colums (as well if only some
columns in the constraint list are nullable) and treat nulls in unique indexes as normal values
(i.e. only one row with null values in indexed columns may be inserted into the table). This
bahavior is very restrictive, does not completely comply with SQL standards (both letter and
intent) as well as with business needs and intending meaning of NULL values (2 null values
are not considered as equal, this comparision shall return NULL, and for selection criteria
boolean null is treated as FALSE).
> This behavior, as far as I can see, is modelled after DB2 (and differs from behavior
of most other major databases, like SyBase, Oracle, etc.).
> But even DB2 provide some means to alleviate these restrictions, namely "UNIQUE WHERE
NOT NULL" clause for CREATE INDEX statement.
> It will be very good if such "UNIQUE WHERE NOT NULL" clause will be introduced in Derby.
> Regards,
> Oleksandr Alesinskyy

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