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Compression [Oracle]

Since 9iR2, Oracle allows to compress tables, materialized views, partitioned tables, index organized tables, btree-indexes and partitioned indexes.
The compression can either be declared for a tablespace, a table or a partitioned table. 
create tablespace ts_compressed 
  datafile 'compressed_01.dbf' size 100m
  default compress storage (10);   

create table compressed_tbl(a number, b varchar2(10)) compress;

  Table compression eliminates duplicate values <i>within</i> a <a href='http://www.adp-gmbh.ch/ora/concepts/db_block.html'>db block</a>. That is, if a table has no repeated values, the compression will be of no use.