sql-server – SELECT语句中的OPTION FAST有什么浸染？

我已经做了一些发掘OPTION(FAST XXX)查询提醒在SELECT语句中做了什么,而且如故对它感想狐疑.按照MSDN：

Specifies that the query is optimized for fast retrieval of the first number_rows. This is a nonnegative integer. After the first number_rows are returned,the query continues execution and produces its full result set.

对我来说没有多大意义,但根基上查询可以真正快速得到前XXX行,然后以正常速率得到别的的行？

让我思索的Microsoft Dynamics查询是：

select pjproj.project,pjproj.project_desc,pjproj.customer,pjproj.cpnyid
from pjproj WITH (NOLOCK)
where project like  '%'
order by project OPTION(FAST 500)

任何人都可以精确地表明这个查询提醒正在做什么,它比不行使它更有上风吗？

办理要领

请留意,预计将凭证N,由于您汇报sql server尽也许快地检索N行.

譬喻在500以下的查询下运行：

-- total rows : 19972
 SELECT [BusinessEntityID],[TotalPurchaseYTD],[DateFirstPurchase],[BirthDate],[MaritalStatus],[YearlyIncome],[Gender],[TotalChildren],[NumberChildrenAtHome],[Education],[Occupation],[HomeOwnerFlag],[NumberCarsOwned]
  FROM [AdventureWorks2012].[Sales].[vPersonDemographics]
  order by BusinessEntityID
  option (fast 500)

Est与现实施选项(快速500)

Est与没有选项的现实施(快速500)

用例是当应用措施正在举办缓存(在靠山加载大量数据)并但愿尽快向用户表现一片数据时.

另一个风趣的用例是在SSIS land that Rob Farley中描写了行使FAST N作为加快数据检索的催化剂.

By adding this hint,it felt like a magic wand had been waved across the query,to make it run several times faster.

见Remus Rusanu’s answer as well.

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