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https://issues.apache.org/jira/browse/DERBY-2212?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16235031#comment-16235031
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Rick Hillegas commented on DERBY-2212:
--------------------------------------
Can you describe your use case which is not satisfied by the work on DERBY-3330
(allowing nullable columns in unique constraints)? Unique constraints now
behave as seen in the following script:
{noformat}
connect 'jdbc:derby:memory:db;create=true';
create table t(a int, b int, unique(a, b));
insert into t(a) values (1);
insert into t values (1, 1);
insert into t(b) values (1);
--succeeds
insert into t(a) values (1);
-- fails: The statement was aborted because it would have caused a duplicate
key value
insert into t values (1, 1);
-- succeeds
insert into t(b) values (1);
-- returns
--
-- 1 1
-- 1 NULL
-- 1 NULL
-- NULL 1
-- NULL 1
--
select * from t order by a, b;
{noformat}
Thanks,
-Rick
> 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
> Priority: Major
> Labels: derby_triage10_10
> Attachments: FunctionalSpec.html, FunctionalSpecV3.html,
> FunctionalSpecV3_comment.html, FunctionlaSpecv2.html, 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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