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  3. March 2007

SQL, Logical Files, Unions & Indexes.

I'm curious (and confused) about the following scenario:
We have an embedded SQL which selects records from a number of files over a number of libraries in order to provide a nationwide view of a business function.
The files are duplicate objects in different libraries, each library representing a state, and of course containing data pertaining to the state represented by the library. 

The SQL brings all the data together into one ODP.
I thought we could speed it up by creating an index as advised by the index advisor, but of course an index can only be created over a single table.
However a logical file can be built over a number of files each in different libraries.
If I create the logical however, I understand that SQL will route the request to the CQE instead of the SQE if a logical file is used and we would take a 15-20% hit (according to a tuning red-book I read)
Are there any benefits to using a logical to provide an index or should we just create an index in every library we want to access the file from? 


On a more philosophical note:
I get the impression that if we had a pure SQL based environment - in other words if only SQL tables, views, and indexes were used - then a programmer should only create the table required to hold the data, and a DBA would then create the views and indexes required to support the functions required? 

Thanks In Advance

Regards,
Mike Pantzopoulos

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