小编Rez*_*dro的帖子

好吧,问题不是真正"如何避免"排序,因为它是业务逻辑所要求的,而是如何使用索引进行初步预测,而不是随时随地.

我有一个查询计划:

|--Sort(TOP 5, ORDER BY:([this_].[DateAdded] DESC))
   |--Nested Loops(Inner Join, OUTER REFERENCES:([this_].[Id], [Expr1002]) OPTIMIZED WITH UNORDERED PREFETCH)
        |--Index Seek(OBJECT:([storm].[dbo].[Items].[IX_Items_ByLocationSorted] AS [this_]), SEEK:([this_].[Status]=(1) AND [this_].[RegionId]=(32) AND [this_].[LocationId]=(32001)),  WHERE:([storm].[dbo].[Items].[SubcategoryTypeId] as [this_].[SubcategoryTypeId]=(88) AND ([storm].[dbo].[Items].[IsHidden] as [this_].[IsHidden]<(1) OR [storm].[dbo].[Items].[IsHidden] as [this_].[IsHidden]>(1))) ORDERED FORWARD)
        |--Clustered Index Seek(OBJECT:([storm].[dbo].[Items].[PK_Items] AS [this_]), SEEK:([this_].[Id]=[storm].[dbo].[Items].[Id] as [this_].[Id]) LOOKUP ORDERED FORWARD) 

您可以看到,Index Seek操作返回一组行.比查询优化器执行密钥查找以检索整行(因为他无论如何都必须返回它),而不是按DateAdded列对所有这些行进行排序.这是一个明显且完全有效的行为.但考虑到Index Seek(最大30k)返回的行数,它确实很慢(可能需要40秒).

如何加快查询速度并避免这种随时随地的排序？

PS:查询表有大约300万行,并且经常更新.这可能会导致页面锁定,但我不认为这些锁定可以持续40秒.

查询:

SELECT TOP 5 * 
FROM Items 
WHERE 
     SubcategoryTypeId = 88 
     and RegionId = 32
 and LocationId = 32001
 and not (IsHidden = 1 and …