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Browse Prior Art Database

Unique Fan-Out Join

IP.com Disclosure Number: IPCOM000102203D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 66K

Publishing Venue

IBM

Related People

Bestgen, RJ: AUTHOR [+5]

Abstract

A new join attribute has been defined that causes a join to occur only if there is one record in the secondary file that will join to a particular record in the primary, or preceding secondary. A record that participates in more than one join is not considered part of the join file.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 76% of the total text.

Unique Fan-Out Join

       A new join attribute has been defined that causes a join
to occur only if there is one record in the secondary file that will
join to a particular record in the primary, or preceding secondary.
A record that participates in more than one join is not considered
part of the join file.

      Defining an equal join between File1 and File2 (Fig. 1) as
unique fan-out would return two records, which are record 2 from
File1 joined to record 9 from File2, and record 4 from File1 joined
to record 3 from File2.  This new type of join eliminates unnecessary
retrievals and allows the user to only see the unique join records.
The decision about uniqueness of the join is left to the underlying
implementation of the join.

      A sort/merge type of join algorithm involves sorting the join
files over the column being used in the join.  The results of the
sort are then merged together.  To implement unique fan-out join
using this type of join algorithm on an equal join, you would
eliminate records in the secondary file that have equal values in
their join columns during the sort phase.  For a join relationship
other than equal (i.e., less than, greater than), you would wait
until the merge phase and then not join records from the secondary if
there was an adjacent one that also joined to the primary record.
Fig. 2 illustrates how unique fan-out works for a sort/merge equal
join.

      A nested-loop-type join requires that an index exist over...