考虑以下查询：
CREATE PROC dbo.GetPage @orderid AS INT = 0, -- anchor sort key
@pagesize AS BIGINT = 25
AS
SELECT
TOP (@pagesize) orderid, orderdate, custid, empid
FROM dbo.Orders WHERE orderid > @orderid ORDER BY orderid;
exec GetPage 25,25返回上述查询的SET STATISTICS IO：
(25 row(s) affected)
Table 'Orders'. Scan count 1, logical reads 87, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.以上阅读内容来自Itzik Ben-Gan的书中的解释是这样的：
执行查询计划所涉及的I / O成本由以下各项组成：
- 寻求索引的叶子：3次读取（索引具有三个级别）。
- 25行的范围扫描：0-1读取（一页中可容纳数百行）。
- 用于优化查找的嵌套循环预取：9次读取（通过使用跟踪标记8744禁用预取来衡量）
- 25个关键查询：75次读取
查询计划
现在我的问题是，由于嵌套循环会对查找返回的每一行进行一次键查找，因此查找读取应为25 * 3：75，与键查找相同吗？
查询计划XML
<?xml version="1.0" encoding="utf-16"?>
<ShowPlanXML xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Version="1.4" Build="13.0.900.73" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
<BatchSequence>
<Batch>
<Statements>
<StmtSimple StatementCompId="3" StatementEstRows="25" StatementId="1" StatementOptmLevel="FULL" StatementOptmEarlyAbortReason="GoodEnoughPlanFound" CardinalityEstimationModelVersion="130" StatementSubTreeCost="0.0887816" StatementText=" CREATE PROC dbo.GetPage @orderid AS INT = 0, -- anchor sort key 
 @pagesize AS BIGINT = 25 
 AS
SELECT TOP (@pagesize) orderid, orderdate, custid, empid FROM dbo.Orders WHERE orderid > @orderid ORDER BY orderid" StatementType="SELECT" QueryHash="0x48DC1D1D4649B914" QueryPlanHash="0x8FDC055F05E0E93C" RetrievedFromCache="true" SecurityPolicyApplied="false">
<StatementSetOptions ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="true" />
<QueryPlan CachedPlanSize="32" CompileTime="2" CompileCPU="2" CompileMemory="208">
<MemoryGrantInfo SerialRequiredMemory="0" SerialDesiredMemory="0" />
<OptimizerHardwareDependentProperties EstimatedAvailableMemoryGrant="52428" EstimatedPagesCached="13107" EstimatedAvailableDegreeOfParallelism="2" />
<RelOp AvgRowSize="29" EstimateCPU="2.5E-06" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="25" LogicalOp="Top" NodeId="0" Parallel="false" PhysicalOp="Top" EstimatedTotalSubtreeCost="0.0887816">
<OutputList>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="custid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="empid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
</OutputList>
<Top RowCount="false" IsPercent="false" WithTies="false">
<TopExpression>
<ScalarOperator ScalarString="[@pagesize]">
<Identifier>
<ColumnReference Column="@pagesize" />
</Identifier>
</ScalarOperator>
</TopExpression>
<RelOp AvgRowSize="29" EstimateCPU="4.1799" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="25" LogicalOp="Inner Join" NodeId="1" Parallel="false" PhysicalOp="Nested Loops" EstimatedTotalSubtreeCost="0.0887791">
<OutputList>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="custid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="empid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
</OutputList>
<NestedLoops Optimized="false" WithOrderedPrefetch="true">
<OuterReferences>
<ColumnReference Column="Uniq1001" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
<ColumnReference Column="Expr1003" />
</OuterReferences>
<RelOp AvgRowSize="18" EstimateCPU="1.10013" EstimateIO="1.92683" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="25" LogicalOp="Index Seek" NodeId="3" Parallel="false" PhysicalOp="Index Seek" EstimatedTotalSubtreeCost="0.00335567" TableCardinality="1000000">
<OutputList>
<ColumnReference Column="Uniq1001" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
</OutputList>
<IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Column="Uniq1001" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderid" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
</DefinedValue>
</DefinedValues>
<Object Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Index="[PK_Orders]" IndexKind="NonClustered" Storage="RowStore" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<StartRange ScanType="GT">
<RangeColumns>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderid" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="[@orderid]">
<Identifier>
<ColumnReference Column="@orderid" />
</Identifier>
</ScalarOperator>
</RangeExpressions>
</StartRange>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
<RelOp AvgRowSize="22" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="25" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="1" LogicalOp="Clustered Index Seek" NodeId="5" Parallel="false" PhysicalOp="Clustered Index Seek" EstimatedTotalSubtreeCost="0.0853189" TableCardinality="1000000">
<OutputList>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="custid" />
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="empid" />
</OutputList>
<IndexScan Lookup="true" Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="custid" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="empid" />
</DefinedValue>
</DefinedValues>
<Object Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Index="[idx_cl_od]" TableReferenceId="-1" IndexKind="Clustered" Storage="RowStore" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<Prefix ScanType="EQ">
<RangeColumns>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
<ColumnReference Column="Uniq1001" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="[PerformanceV3].[dbo].[Orders].[orderdate]">
<Identifier>
<ColumnReference Database="[PerformanceV3]" Schema="[dbo]" Table="[Orders]" Column="orderdate" />
</Identifier>
</ScalarOperator>
<ScalarOperator ScalarString="[Uniq1001]">
<Identifier>
<ColumnReference Column="Uniq1001" />
</Identifier>
</ScalarOperator>
</RangeExpressions>
</Prefix>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
</NestedLoops>
</RelOp>
</Top>
</RelOp>
<ParameterList>
<ColumnReference Column="@pagesize" ParameterCompiledValue="(25)" />
<ColumnReference Column="@orderid" ParameterCompiledValue="(25)" />
</ParameterList>
</QueryPlan>
</StmtSimple>
</Statements>
</Batch>
</BatchSequence>
</ShowPlanXML>