Attribute clustering that is based on joined columns is called join attribute clustering. In contrast with table clusters, join attribute clustered tables do not store data from a group of tables in the same database blocks.

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For example, consider an attribute-clustered table, sales, joined with a dimension table, products. The sales table contains only rows from the sales table, but the ordering of the rows is based on the values of columns joined from products table. The appropriate join is executed during data movement, direct path insert, and CREATE TABLE AS SELECT operations. In contrast, if sales and products were in a standard table cluster, the data blocks would contain rows from both tables.

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See also

Oracle Database Data Warehousing Guide to learn more about join attribute clustering

I/O Reduction Using Zones

A zone is a set of contiguous data blocks that stores the minimum and maximum values of relevant columns. When a SQL statement contains predicates on columns stored in a zone, the database compares the predicate values to the minimum and maximum stored in the zone to determine which zones to read during SQL execution.

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I/O reduction is the ability to skip table or index blocks that do not contain data that the database needs to satisfy the query. This reduction can significantly reduce the I/O and CPU cost of table scans.

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