最大区别在于clustered是物理上实现数据排序，并且同一个表里只能有一个clustered索引，而nonclustered是逻辑上的排序。
There are clustered and nonclustered indexes. A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table can have only one clustered index. The leaf nodes of a clustered index contain the data pages.
A nonclustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk. The leaf node of a nonclustered index does not consist of the data pages. Instead, the leaf nodes contain index rows.
本文出自：冯立彬的博客
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