Sql server SQL Server查询计划，运行时间较短，但子树成本较高
为什么下面两个查询中的第一个查询的运行时间较低，而估计的子树成本较高 估计子树成本只是与其他查询性能指标（如响应时间）一起衡量查询计划性能的一个指南，但我很惊讶在并排比较两个类似的查询时，成本和时间之间存在反比关系 我创建了一个示例数据库来说明这个问题，并包含了两个查询的结果XML查询计划。我意识到StateID作为外键存在于County和Town表中是一种糟糕的形式，但这是我解释这种现象最简单的方法 我不是在问“哪一个更重要，子树成本还是响应时间”。我想了解两个类似查询的查询计划子树成本和响应时间之间如何存在反向关系，以便我能够做出更明智的决策 请注意，下面的两个查询产生完全相同的结果集 谢谢Sql server SQL Server查询计划，运行时间较短，但子树成本较高,sql-server,sql-execution-plan,Sql Server,Sql Execution Plan,为什么下面两个查询中的第一个查询的运行时间较低，而估计的子树成本较高 估计子树成本只是与其他查询性能指标（如响应时间）一起衡量查询计划性能的一个指南，但我很惊讶在并排比较两个类似的查询时，成本和时间之间存在反比关系 我创建了一个示例数据库来说明这个问题，并包含了两个查询的结果XML查询计划。我意识到StateID作为外键存在于County和Town表中是一种糟糕的形式，但这是我解释这种现象最简单的方法 我不是在问“哪一个更重要，子树成本还是响应时间”。我想了解两个类似查询的查询计划子树成本和响应
CREATE TABLE dbo.County (StateID INT, CountyID INT)
CREATE TABLE dbo.Town (StateID INT, CountyID INT, TownID INT)
DECLARE @State TABLE (StateID INT, PRIMARY KEY CLUSTERED (StateID))
DECLARE @County TABLE (CountyID INT, PRIMARY KEY CLUSTERED (CountyID))
INSERT INTO @State
VALUES (27)
INSERT INTO @County
SELECT DISTINCT
c.CountyID
FROM dbo.County c
JOIN @State s ON c.StateID = s.StateID
-- low time, high cost query
SELECT DISTINCT
t.CountyID,
t.TownID
FROM dbo.Town t
JOIN @State s
ON t.StateID = s.StateID
-- low cost, high time query
SELECT DISTINCT
t.CountyID,
t.TownID
FROM dbo.Town t
JOIN @State s
ON t.StateID = s.StateID
JOIN @County c
ON t.CountyID = c.CountyID
<StmtSimple StatementCompId="6" StatementEstRows="273495" StatementId="3" StatementOptmLevel="FULL" StatementSubTreeCost="6.06304" StatementText="SELECT DISTINCT
	t.CountyID,
	t.TownID
FROM dbo.Town t
JOIN @State s
	ON t.StateID = s.StateID

-- low cost, high time query
" StatementType="SELECT" QueryHash="0x9347C19165C31DBF" QueryPlanHash="0x98EE57C66D8B347A">
<StatementSetOptions ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="true" />
<QueryPlan DegreeOfParallelism="2" MemoryGrant="28144" CachedPlanSize="32" CompileTime="8" CompileCPU="8" CompileMemory="312">
<RelOp AvgRowSize="15" EstimateCPU="0.388488" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="273495" LogicalOp="Gather Streams" NodeId="0" Parallel="true" PhysicalOp="Parallelism" EstimatedTotalSubtreeCost="6.06304">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="13027" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<Parallelism>
<RelOp AvgRowSize="15" EstimateCPU="3.79725" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="273495" LogicalOp="Aggregate" NodeId="1" Parallel="true" PhysicalOp="Hash Match" EstimatedTotalSubtreeCost="5.67455">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<MemoryFractions Input="0.998723" Output="1" />
<RunTimeInformation>
<RunTimeCountersPerThread Thread="2" ActualRows="6515" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="1" ActualRows="6512" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<Hash>
<DefinedTowns />
<HashKeysBuild>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</HashKeysBuild>
<BuildResidual>
<ScalarOperator ScalarString="[Locality].[dbo].[Town].[CountyID] as [t].[CountyID] = [Locality].[dbo].[Town].[CountyID] as [t].[CountyID] AND [Locality].[dbo].[Town].[TownID] as [t].[TownID] = [Locality].[dbo].[Town].[TownID] as [t].[TownID]">
<Logical Operation="AND">
<ScalarOperator>
<Compare CompareOp="IS">
<ScalarOperator>
<Identifier>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</Identifier>
</ScalarOperator>
<ScalarOperator>
<Identifier>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</Identifier>
</ScalarOperator>
</Compare>
</ScalarOperator>
<ScalarOperator>
<Compare CompareOp="IS">
<ScalarOperator>
<Identifier>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</Identifier>
</ScalarOperator>
<ScalarOperator>
<Identifier>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</Identifier>
</ScalarOperator>
</Compare>
</ScalarOperator>
</Logical>
</ScalarOperator>
</BuildResidual>
<RelOp AvgRowSize="15" EstimateCPU="0.494228" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="273495" LogicalOp="Repartition Streams" NodeId="2" Parallel="true" PhysicalOp="Parallelism" EstimatedTotalSubtreeCost="1.8773">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="2" ActualRows="1017328" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="1" ActualRows="1093191" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<Parallelism PartitioningType="Hash">
<PartitionColumns>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</PartitionColumns>
<RelOp AvgRowSize="15" EstimateCPU="0.571604" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="273495" LogicalOp="Inner Join" NodeId="3" Parallel="true" PhysicalOp="Nested Loops" EstimatedTotalSubtreeCost="1.38307">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="2" ActualRows="0" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="1" ActualRows="2110519" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<NestedLoops Optimized="true">
<OuterReferences>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</OuterReferences>
<RelOp AvgRowSize="11" EstimateCPU="0.0285019" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Distribute Streams" NodeId="5" Parallel="true" PhysicalOp="Parallelism" EstimatedTotalSubtreeCost="0.031785">
<OutputList>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="2" ActualRows="0" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="1" ActualRows="1" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<Parallelism PartitioningType="RoundRobin">
<RelOp AvgRowSize="11" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Clustered Index Scan" NodeId="6" Parallel="false" PhysicalOp="Clustered Index Scan" EstimatedTotalSubtreeCost="0.0032831" TableCardinality="0">
<OutputList>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="1" ActualRows="1" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<IndexScan Ordered="false" ForcedIndex="false" NoExpandHint="false">
<DefinedTowns>
<DefinedTown>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</DefinedTown>
</DefinedTowns>
<Object Table="[@State]" Index="[PK__#3AB788A__C3BA3B5A3C9FD11A]" Alias="[s]" />
</IndexScan>
</RelOp>
</Parallelism>
</RelOp>
<RelOp AvgRowSize="15" EstimateCPU="0.301001" EstimateIO="0.478681" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="273495" LogicalOp="Index Seek" NodeId="7" Parallel="true" PhysicalOp="Index Seek" EstimatedTotalSubtreeCost="0.779682" TableCardinality="6291320">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="2" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
<RunTimeCountersPerThread Thread="1" ActualRows="2110519" ActualEndOfScans="1" ActualExecutions="1" />
<RunTimeCountersPerThread Thread="0" ActualRows="0" ActualEndOfScans="0" ActualExecutions="0" />
</RunTimeInformation>
<IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" ForceSeek="false" NoExpandHint="false">
<DefinedTowns>
<DefinedTown>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</DefinedTown>
<DefinedTown>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</DefinedTown>
</DefinedTowns>
<Object Database="[Locality]" Schema="[dbo]" Table="[Town]" Index="[NCX_Town_StateID_CountyID_TownID]" Alias="[t]" IndexKind="NonClustered" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<Prefix ScanType="EQ">
<RangeColumns>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="StateID" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="@State.[StateID] as [s].[StateID]">
<Identifier>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</Identifier>
</ScalarOperator>
</RangeExpressions>
</Prefix>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
</NestedLoops>
</RelOp>
</Parallelism>
</RelOp>
</Hash>
</RelOp>
</Parallelism>
</RelOp>
</QueryPlan>
</StmtSimple>
<StmtSimple StatementCompId="7" StatementEstRows="339.324" StatementId="4" StatementOptmLevel="FULL" StatementOptmEarlyAbortReason="GoodEnoughPlanFound" StatementSubTreeCost="0.142839" StatementText="SELECT DISTINCT
	t.CountyID,
	t.TownID
FROM dbo.Town t
JOIN @State s
	ON t.StateID = s.StateID
JOIN @County c
	ON t.CountyID = c.CountyID

" StatementType="SELECT" QueryHash="0xF7B13FA8059B141C" QueryPlanHash="0x31CEE9DAF12E77A5">
<StatementSetOptions ANSI_NULLS="true" ANSI_PADDING="true" ANSI_WARNINGS="true" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="true" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="true" />
<QueryPlan DegreeOfParallelism="1" MemoryGrant="1584" CachedPlanSize="40" CompileTime="5" CompileCPU="5" CompileMemory="376">
<RelOp AvgRowSize="15" EstimateCPU="0.00454996" EstimateIO="0.0112613" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="339.324" LogicalOp="Distinct Sort" NodeId="0" Parallel="false" PhysicalOp="Sort" EstimatedTotalSubtreeCost="0.142839">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<MemoryFractions Input="1" Output="1" />
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRebinds="1" ActualRewinds="0" ActualRows="13027" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<Sort Distinct="true">
<OrderBy>
<OrderByColumn Ascending="true">
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</OrderByColumn>
<OrderByColumn Ascending="true">
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OrderByColumn>
</OrderBy>
<RelOp AvgRowSize="15" EstimateCPU="0.0571741" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="339.324" LogicalOp="Inner Join" NodeId="1" Parallel="false" PhysicalOp="Hash Match" EstimatedTotalSubtreeCost="0.127028">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<MemoryFractions Input="0" Output="0" />
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="2110519" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<Hash>
<DefinedTowns />
<HashKeysBuild>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</HashKeysBuild>
<HashKeysProbe>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="StateID" />
</HashKeysProbe>
<RelOp AvgRowSize="11" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Clustered Index Scan" NodeId="2" Parallel="false" PhysicalOp="Clustered Index Scan" EstimatedTotalSubtreeCost="0.0032831" TableCardinality="0">
<OutputList>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="1" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<IndexScan Ordered="false" ForcedIndex="false" NoExpandHint="false">
<DefinedTowns>
<DefinedTown>
<ColumnReference Table="@State" Alias="[s]" Column="StateID" />
</DefinedTown>
</DefinedTowns>
<Object Table="[@State]" Index="[PK__#3AB788A__C3BA3B5A3C9FD11A]" Alias="[s]" />
</IndexScan>
</RelOp>
<RelOp AvgRowSize="19" EstimateCPU="0.0357739" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="8558.34" LogicalOp="Inner Join" NodeId="3" Parallel="false" PhysicalOp="Nested Loops" EstimatedTotalSubtreeCost="0.066568">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="StateID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="2110519" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<NestedLoops Optimized="false">
<OuterReferences>
<ColumnReference Table="@County" Alias="[c]" Column="CountyID" />
</OuterReferences>
<RelOp AvgRowSize="11" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Clustered Index Scan" NodeId="4" Parallel="false" PhysicalOp="Clustered Index Scan" EstimatedTotalSubtreeCost="0.0032831" TableCardinality="0">
<OutputList>
<ColumnReference Table="@County" Alias="[c]" Column="CountyID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="137" ActualEndOfScans="1" ActualExecutions="1" />
</RunTimeInformation>
<IndexScan Ordered="false" ForcedIndex="false" NoExpandHint="false">
<DefinedTowns>
<DefinedTown>
<ColumnReference Table="@County" Alias="[c]" Column="CountyID" />
</DefinedTown>
</DefinedTowns>
<Object Table="[@County]" Index="[PK__#3E88198__B68F9DF7407061FE]" Alias="[c]" />
</IndexScan>
</RelOp>
<RelOp AvgRowSize="19" EstimateCPU="0.00957118" EstimateIO="0.0179398" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="8558.34" LogicalOp="Index Seek" NodeId="5" Parallel="false" PhysicalOp="Index Seek" EstimatedTotalSubtreeCost="0.027511" TableCardinality="6291320">
<OutputList>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="StateID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</OutputList>
<RunTimeInformation>
<RunTimeCountersPerThread Thread="0" ActualRows="2110519" ActualEndOfScans="137" ActualExecutions="137" />
</RunTimeInformation>
<IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" ForceSeek="false" NoExpandHint="false">
<DefinedTowns>
<DefinedTown>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="StateID" />
</DefinedTown>
<DefinedTown>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</DefinedTown>
<DefinedTown>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="TownID" />
</DefinedTown>
</DefinedTowns>
<Object Database="[Locality]" Schema="[dbo]" Table="[Town]" Index="[NCX_Town_CountyID_inc_StateID_TownID]" Alias="[t]" IndexKind="NonClustered" />
<SeekPredicates>
<SeekPredicateNew>
<SeekKeys>
<Prefix ScanType="EQ">
<RangeColumns>
<ColumnReference Database="[Locality]" Schema="[dbo]" Table="[Town]" Alias="[t]" Column="CountyID" />
</RangeColumns>
<RangeExpressions>
<ScalarOperator ScalarString="@County.[CountyID] as [c].[CountyID]">
<Identifier>
<ColumnReference Table="@County" Alias="[c]" Column="CountyID" />
</Identifier>
</ScalarOperator>
</RangeExpressions>
</Prefix>
</SeekKeys>
</SeekPredicateNew>
</SeekPredicates>
</IndexScan>
</RelOp>
</NestedLoops>
</RelOp>
</Hash>
</RelOp>
</Sort>
</RelOp>
</QueryPlan>
</StmtSimple>