Databases Reference
In-Depth Information
CHAPTER 4
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Index-Organized Tables
The simplest explanation of an index-organized table is that it is accessed like any other Oracle table
(typically a heap-organized table) but is physically stored like an Oracle B-tree index. Index-organized
tables are typically created on "thin" tables (tables without too many columns). Typically, multiple
columns of the table make up the primary key of the index-organized table. The non-key columns can
also be stored as part of the B-tree index. The proper configuration and use of index-organized tables is
fairly specific and does not meet all application needs.
Understanding the Structure
From a user or developer perspective, an index-organized table (IOT) appears like a normal table. IOTs
are stored in a B-tree structure. There must be a primary key on an index-organized table, as the data is
stored in primary key order. Since there is no data segment, there is no physical
ROWID
values for index-
organized tables. See Figure 4-1 for an example of an IOT.
Figure 4-1. Structure of an index-organized table
