db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mike Matrigali (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-2212) Add "Unique where not null" to create index
Date Tue, 20 Nov 2007 18:44:43 GMT

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

Mike Matrigali updated DERBY-2212:
----------------------------------


I do want to say that once it is clear what the functionality is being provided, it would
be great to then write up the implementation details on how we are going to achieve that functionality.
 I requested we first concentrate on 
the functionality as it was not clear to me at all what was being implemented - just a patch
that did something
to index internals.  It was impossible for me to comment on the proposed implementation without
understanding what
the actual change wanted to accomplish.  

I think I now understand the functionality being proposed, though the spec could use a little
gramatical cleanup.  I
have also in the discussion given one approach that I believe will fit well with the existing
system to implement 
the new unique constraint with nulls functionality.  

I did not mean to stifle the implementation discussion/writeup - I just wanted to first understand
what the proposed
functionality was.  I may have been imposing my closed source background where functional
specs and implementation specs were always 2 different documents and were written/discussed/reviewed
separately.  



> 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

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.


Mime
View raw message