Index-Organized Table

An Oracle index-organized Table is a table stored in an index B-Tree structure. There is no second data structure (heap-table) for the table. The Oracle database always uses the primary key as clustering key. An Index-Organized Table is created with the ORGANIZATION INDEX clause:

CREATE TABLE (
   id    NUMBER NOT NULL PRIMARY KEY,
   [...]
) ORGANIZATION INDEX

Accessing table data via a secondary index is slower than a similar query on a heap-table.

SQL Server supports index-organized tables as well, but uses the term clustered index.