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Oracle Data Warehouse Tuning for 10g
book

Oracle Data Warehouse Tuning for 10g

by Gavin JT Powell
April 2011
Intermediate to advanced content levelIntermediate to advanced
504 pages
16h 49m
English
Digital Press
Content preview from Oracle Data Warehouse Tuning for 10g
168
7.1
Basic Query Tuning
Figure 7.8 shows the same query as in Figures 7.6 and 7.7, but with the
first two prefix columns for the index. The index is used even though the
third column is omitted from the WHERE clause. The optimizer considers
using the index the best option, because much fewer rows are read than for
the query in Figure 7.7, where only a single column of the index was used.
An index skip scan is used in Figure 7.9, where prefix index columns can
be skipped. An index skip scan is a special type of index read that can utilize
subset columns of composite indexes, where perhaps the first column in a
multiple column composite index is not required ...
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Publisher Resources

ISBN: 9781555583354