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Overview of Index-Organized Tables (227)

原创 网络安全 作者:tsinglee 时间:2007-11-20 11:07:03 0 删除 编辑

An index-organized table has a storage organization that is a variant of a primary
B-tree. Unlike an ordinary (heap-organized) table whose data is stored as an
unordered collection (heap), data for an index-organized table is stored in a B-tree
index structure in a primary key sorted manner. Besides storing the primary key
column values of an index-organized table row, each index entry in the B-tree stores
the nonkey column values as well.

The index-organized table is somewhat similar to a configuration consisting of an ordinary table and
an index on one or more of the table columns, but instead of maintaining two separate storage
structures, one for the table and one for the B-tree index, the database system maintains only a
single B-tree index. Also, rather than having a row's rowid stored in the index entry, the nonkey
column values are stored. Thus, each B-tree index entry contains non_primary_key_column_values>.


索引组织表
1. 索引组织表中的数据存储在依据主键排序的平衡树索引结构中 ,不仅存储索引表各行的主键列值,
同时也存储各行的非键列值
2. 索引表包含的内容可以看作由两部分构成:一个常规的表;一个建于此表一列或多列上的平衡树索引。
Oracle不会将组成索引表的表和索引作为两个分离的逻辑结构,而是将整个索引表存储为一个平衡树索引。
在索引表中,每个索引项中不会存储 rowid,而是直接存储非键列值。
即每个平衡树索引项中包含 主键列 和 非主键列

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