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https://issues.apache.org/jira/browse/DERBY-3748?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mamta A. Satoor updated DERBY-3748:
-----------------------------------
Urgency: Normal
Labels: derby_triage10_10 (was: )
> add support to create indexes on non key fields
> -----------------------------------------------
>
> Key: DERBY-3748
> URL: https://issues.apache.org/jira/browse/DERBY-3748
> Project: Derby
> Issue Type: Improvement
> Components: SQL, Store
> Affects Versions: 10.4.1.3
> Reporter: Mike Matrigali
> Priority: Minor
> Labels: derby_triage10_10
>
> Add support to CREATE INDEX on non key fields.
> Often query execution can be improved by creating indexes that include all
> the columns that are returned by the query (referred to as a "covering"
> index).
> Currently in Derby to do this one must make all the fields part of the key,
> but often the requirements of the query only need part of these columns to
> be keyed. By making them part of the key it increases the size of the key
> that is used in the non-key part of the index structure resulting in more
> search overhead (both cpu and disk space), than is necessary.
> The existing btree code has some framework already for non-key fields so a
> major rework should not be necessary, but would not be surprised if some
> issues still remain. Things to resolve as part of this work:
> 1) what part of sql to change, maybe just CREATE INDEX.
> 2) are there any optimizer/execution issues with the new type of index? any
> metadata changes necessary to track key vs. non-key fields?
> 3) current btree code assumes non-key fields are at end, and use non-key
> field stuff for unique vs. non-unique indexes.
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