Reasons not to have a clustered index in SQL Server 2005

Question

I\'ve inherited some database creation scripts for a SQL SERVER 2005 database.

One thing I\'ve noticed is that all primary keys are created as NON CLUSTERED

Answer 1

Clustered Tables vs Heap Tables

(Good article on subject at www.mssqltips.com)

HEAP Table (Without clustered index)

• Data is not stored in any particular order

• Specific data can not be retrieved quickly, unless there are also non-clustered indexes

• Data pages are not linked, so sequential access needs to refer back to the index allocation map (IAM) pages

• Since there is no clustered index, additional time is not needed to maintain the index

• Since there is no clustered index, there is not the need for additional space to store the clustered index tree

• These tables have a index_id value of 0 in the sys.indexes catalog view

Clustered Table

• Data is stored in order based on the clustered index key

• Data can be retrieved quickly based on the clustered index key, if the query uses the indexed columns

• Data pages are linked for faster sequential access Additional time is needed to maintain clustered index based on INSERTS, UPDATES and DELETES

• Additional space is needed to store clustered index tree These tables have a index_id value of 1 in the sys.indexes catalog view