A clustered index in sql server like a dictionary or telephone directory. A,B,C,D it goes on.
If you look up with a name Ozgur you start O then z etc.

I would like a simple explaination for this concept for oracle savy users.

More information about Clustered Indexes in Sql Server. What is a Clustered Index?


In Oracle terminology, it is an Index Organized Table, commonly referred to as an IOT.

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. Each leaf block in the index structure stores both the key and nonkey columns.

| improve this answer | |
  • 1
    It is probably the closest thing to a clustered index, but it sure isn't the same thing. – a_horse_with_no_name Nov 16 '11 at 9:49
  • @a_horse_with_no_name How do they differ? – Mark Storey-Smith Nov 16 '11 at 9:53
  • 2
    Hi horse! IN SQL Server the clustered index also is physically the table - the table data is physically stored in the index. – Niall Litchfield Nov 16 '11 at 11:12
  • 1
    @a_horse_with_no_name, after reading on IOTs, it's exactly the same thing as clustered indexes in SQL Server: a B-Tree with the index keys, and sorted leaves by the index keys. download.oracle.com/docs/cd/E14072_01/server.112/e10713/… – gonsalu Nov 16 '11 at 11:57
  • 1
    @Gonsalu: but one of the differences is still that SQL Server can create a clustered index on non-unique (i.e PK) columns. Btw: I found this page quite interesting: use-the-index-luke.com/sql/clustering/… – a_horse_with_no_name Nov 16 '11 at 13:32

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.