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https://issues.apache.org/jira/browse/DERBY-2212?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali updated DERBY-2212:
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Along the same lines in the case of multi-column keys, what null behavior is
being
implemented? In this bug description I think I have at least seen oracle with
one behavior and
db2/postgres with another.
Can the db2/postgres behavior be implemented as simply as if there is a null in
any column
of a key (either single column or multi-column) don't do any uniqueness
checking on insert
of that row?
> 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
>
>
> 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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