综合指数和覆盖指数之间的差异 [英] difference between a Composite Index and a Covering Index

问题描述

综合指数和覆盖指数之间有什么区别?
请举例说明您必须使用Covering Index，而不能使用Composite Index.
感谢

what is difference between a Composite Index and a Covering Index?
please give example that you must use Covering Index and you can''t use Composite Index instead of that.
Thanks

推荐答案

综合索引 :包含多个列的索引.在SQL Server 2005或更高版本中，只要索引不超过900字节的限制，您最多可以在索引中包括16列.聚簇索引和非聚簇索引都可以是复合索引.

覆盖索引 :一种索引类型，其中包括处理特定查询所需的所有列.例如，您的查询可能基于ContactID列中的值从表中检索FirstName和LastName列.您可以创建一个包含所有三列的覆盖索引.

有关更多详细说明，请参见下面的链接


http://msdn.microsoft.com/zh-CN/library/ms188783.aspx

希望这个breife解释能满足您的要求……

Composite index: An index that contains more than one column. In both SQL Server 2005 or higher, you can include up to 16 columns in an index, as long as the index doesn’t exceed the 900 byte limit. Both clustered and nonclustered indexes can be composite indexes.

Covering index: A type of index that includes all the columns that are needed to process a particular query. For example, your query might retrieve the FirstName and LastName columns from a table, based on a value in the ContactID column. You can create a covering index that includes all three columns.

for more detailed explanation, see below links


http://msdn.microsoft.com/en-us/library/ms188783.aspx

Hope this breife explaniation will meet your requirment......

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