Nonclustered Indexes
A nonclustered index is a separate index structure, independent of the physical sort order of the data rows in the table. You are therefore not restricted to creating only 1 nonclustered index per table; in fact, in SQL Server 2012 you can create up to 999 nonclustered indexes per table. This is an increase from SQL Server 2005, which was limited to 249.
A nonclustered index is analogous to an index in the back of a book. To find the pages on which a specific subject is discussed, you look up the subject in the index and then go to the pages referenced in the index. With nonclustered indexes, you may have to jump around to many different nonsequential pages to find all the references.
A nonclustered index is also structured ...
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