Fred Shen: Adding covering indexes for aggregate function

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Источник: http://fredshen.spaces.live.com/Blog...E4E3!158.entry
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It is always recommended to use aggregate function (like sum, avg, minof, maxof and count) in queries where applicable in Axapta. If you run this kind of query frequently, it is considerable to add a covering index for the query. A covering index is an index, which includes all of the columns referenced in the query.
And what is the reason? Because SQL Server can use these entries in the index's leaf level to perform aggregate calculations. This means that the index contains the data you are looking for, and SQL Server does not have to go to the actual table to perform the aggregate calculations, which can boost performance.




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Источник: http://fredshen.spaces.live.com/Blog...E4E3!158.entry