Overview of Index-Organized Tables (227)

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>.

索引組織表
1. 索引組織表中的資料儲存在依據主鍵排序的平衡樹索引結構中 ，不僅儲存索引表各行的主鍵列值，
同時也儲存各行的非鍵列值
2. 索引表包含的內容可以看作由兩部分構成：一個常規的表；一個建於此表一列或多列上的平衡樹索引。
Oracle不會將組成索引表的表和索引作為兩個分離的邏輯結構，而是將整個索引表儲存為一個平衡樹索引。
在索引表中，每個索引項中不會儲存 rowid，而是直接儲存非鍵列值。
即每個平衡樹索引項中包含 主鍵列 和 非主鍵列

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