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From Mike Matrigali <mikem_...@sbcglobal.net>
Subject Re: partial indexes
Date Fri, 05 Nov 2004 00:36:35 GMT
I don't know much about PostgreSQL, but from a quick google search it
seems a "partial" index is a secondary index maintained on a subset of
the data (partitioned by some sort of where clause predicate).

Derby currently does not support this kind of index.  Currently only
indexes that maintain one-to-one relationship between base table rows
and index rows are supported.

Note that this restriction is not part of the Storage system.  The btree
implementation does not maintain the relationship, and thus could be
used as is to implement such a feature.  The changes necessary would be
to the optimizer to understand how to cost and use such an index and to
the language system to teach it to maintain such an index.

A reasonable building block for such a feature would probably be to
first implement some sort of "functional" index, which would still
provide a one-to-one relationship between base table and index rows but
would index on the values returned by a function as applied to one or
more columns of a single row.


Garbage Collector wrote:

> Does Derby supports partial indexes like that in PostgreSQL or something
> like that?
> Thanks in advance.

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