https://docs.microsoft.com/en-us/sql/relational-databases/indexes/clustered-and-nonclustered-indexes-described

https://msdn.microsoft.com/zh-cn/library/ms190457

https://msdn.microsoft.com/ja-jp/library/ms190639.aspx

https://msdn.microsoft.com/ja-jp/library/ms188385.aspx

https://msdn.microsoft.com/ja-jp/library/ms190639.aspx

http://www.cnblogs.com/CareySon/archive/2011/12/22/2297568.html#!comments