What is a Non-Clustered Index?

Nonclustered Nonclustered indexes have a structure separate from the data rows. A nonclustered index contains the nonclustered index key values and each key value entry has a pointer to the data row that contains the key value. The pointer from an index row in a nonclustered index to a data row is called a row locator. The structure of the row locator depends on whether the data pages are stored in a heap or a clustered table. For a heap, a row locator is a pointer to the row. For a clustered table, the row locator is the clustered index key.

A Non-Clustered index stored in logical order of the index does not match the physical stored order of the row on disk. The leaf node of a Non-Clustered index do not consist of the data pages. Instead the leaf node contain the index row. In Sql 2005 there is 249 Non-Clustered Index. In Sql 2008 there is 999 Non-Clustered Index.