Overview of Index-Organized Tables【每日一译】--20121231

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.

一个索引组织表拥有一个存储结构，它是基本B-TREE索引的变种。不像原始（哈希-组织）表

，它们的数据是一个无序的集合（哈希），数据对于一个索引组织表它存在于一个B-TREE索引

结构在按一个主键排序顺序。除了存储索引组织表行的主键列的值外，每个索引条目在B-TREE

也存储了非主键列的值。

 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 <primary_key_value,
non_primary_key_column_values>.

索引组织表在一些地方类似于由一个原始表和一个在一个或多个表上列的索引构成配置一样，

通过代替两种单独的存储结构，一个是表另一个是B-TREE索引，数据库系统维护仅一个单独

的B-TREE索引。另外不需要包含一个行的ROWID存储在索引条目，非主键列的值也是存储的。

这样，每个B-TREE索引条目包含主键值，非主键列的值。