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https://issues.apache.org/jira/browse/DERBY-3330?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12573108#action_12573108
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Dibyendu Majumdar commented on DERBY-3330:
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Hi,
I could be talking nonsense here so please tell me to shut up if I have got the
wrong end of the issue.
If I understand correctly, one of the requirements is to allow multiple rows to
be inserted where the index is unique and all columns are null. This doesn't
work currently because such rows will be considered duplicates.
Thinking very naively, I would implement this as follows:
I am assuming that when index rows are stored, Derby always stores an
additional column containing the row location, regardless of the type of index.
Also that the search algorithm is uniform for both unique and non-unique
indexes, with the only difference being that the unique index searches do not
consider the extra row location column.
Following is invalid if above assumptions are not true.
To get the desired behaviour, I would simply change the comparison logic as
follows:
a) If non-unique index, no change.
b) If unique index, and all indexable columns are null, then compare the extra
(last) (row location) column.
c) The else case for unique index will remain the same as now.
If the key comparison routine always used above logic, would it not give
desired behaviour without requiring any significant changes to the existing
implementation?
As I said, I may totally off track here, so please feel free to tell me to shut
up.
> provide support for unique constraint over nullable columns
> -----------------------------------------------------------
>
> Key: DERBY-3330
> URL: https://issues.apache.org/jira/browse/DERBY-3330
> Project: Derby
> Issue Type: New Feature
> Components: Store
> Affects Versions: 10.4.0.0
> Environment: all
> Reporter: Anurag Shekhar
> Assignee: Anurag Shekhar
> Attachments: BTreeController.diff, derby-3330-testcase.diff,
> derby-3330.diff, derby-3330v10.diff, derby-3330v2.diff, derby-3330v3.diff,
> derby-3330v4.diff, derby-3330v5.diff, derby-3330v6.diff, derby-3330v7.diff,
> derby-3330v8.diff, derby-3330v9.diff, FunctionalSpec_DERBY-3330-V2.html,
> FunctionalSpec_DERBY-3330.html, UniqueConstraint_Implementation.html,
> UniqueConstraint_Implementation_V2.html,
> UniqueConstraint_Implementation_V3.html
>
>
> Allow unique constraint over nullable field. Right now derby support unique
> constraint only over not null columns.
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