我有一个包含3个内部联接的脚本。似乎当我添加第三个内连接时，脚本运行速度非常慢。前两个表有大约3-4,000行，第三个有63.3万行，最后一个表只有36行。我试过索引，但我没有注意到变化。我在编制索引之前和之后都包含了我的脚本。返回前5个条目大约需要12分钟。如果需要更多信息，请询问。我是数据库管理的新手。
在索引之前：
SELECT DISTINCT TOP 5 sn.NAME, cd.ASSIGNEDPOLICY, cd.COMPANYPOLICYNUMBER, ad.COVERAGECODE, co."DESCRIPTION"
From SNAMES sn
inner join TCUSDTL cd on sn.NAMEID = cd.NAMEID
inner join TPOLACTD ad on sn.NAMEID = ad.NAMEID
inner join SCOVTBL co on ad.COVERAGECODE = co.COVERAGE
ORDER BY NAME
索引后：
SELECT DISTINCT TOP 5 sn.NAME, cd.ASSIGNEDPOLICY, cd.COMPANYPOLICYNUMBER, ad.COVERAGECODE, co."DESCRIPTION"
From SNAMES sn WITH(INDEX(SNAMES_names))
inner join TCUSDTL cd WITH(INDEX(TCUSDTL_policies)) on sn.NAMEID = cd.NAMEID
inner join TPOLACTD ad WITH(INDEX(TPOLACTD_coverage)) on sn.NAMEID = ad.NAMEID
inner join SCOVTBL co WITH(INDEX(SCOVTBL_coverage)) on ad.COVERAGECODE = co.COVERAGE
ORDER BY NAME
执行计划：
<?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="1.5" Build="13.0.703.859" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
<BatchSequence>
<Batch>
<Statements>
<StmtSimple StatementCompId="1" StatementEstRows="1000" StatementId="1" StatementOptmLevel="FULL" CardinalityEstimationModelVersion="120" StatementSubTreeCost="5270.92" StatementText="SELECT DISTINCT TOP 1000 sn.NAME, cd.ASSIGNEDPOLICY, cd.COMPANYPOLICYNUMBER, bd.COVERAGECODE, sd."DESCRIPTION"
FROM SNAMES sn
inner join TCUSDTL cd on sn.NAMEID = cd.NAMEID 
inner join TPOLACTD bd on sn.NAMEID = bd.NAMEID 
inner join SCOVTBL sd on bd.COVERAGECODE = sd.COVERAGE
ORDER BY NAME" StatementType="SELECT" QueryHash="0x5C4838D1FC1E530E" QueryPlanHash="0x854BE2475051DE74" 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 NonParallelPlanReason="EstimatedDOPIsOne" CachedPlanSize="104" CompileTime="27" CompileCPU="26" CompileMemory="1144">
<MemoryGrantInfo SerialRequiredMemory="3584" SerialDesiredMemory="7383960" />
<OptimizerHardwareDependentProperties EstimatedAvailableMemoryGrant="11744005" EstimatedPagesCached="734000" EstimatedAvailableDegreeOfParallelism="1" />
<RelOp AvgRowSize="94" EstimateCPU="0.0001" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="1000" LogicalOp="Top" NodeId="0" Parallel="false" PhysicalOp="Top" EstimatedTotalSubtreeCost="5270.92">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<Top RowCount="false" IsPercent="false" WithTies="false">
<TopExpression>
<ScalarOperator ScalarString="(1000)">
<Const ConstValue="(1000)" />
</ScalarOperator>
</TopExpression>
<RelOp AvgRowSize="94" EstimateCPU="5177.31" EstimateIO="0.0112613" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="1000" LogicalOp="Distinct Sort" NodeId="1" Parallel="false" PhysicalOp="Sort" EstimatedTotalSubtreeCost="5270.92">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<MemoryFractions Input="0.985219" Output="1" />
<Sort Distinct="true">
<OrderBy>
<OrderByColumn Ascending="true">
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
</OrderByColumn>
<OrderByColumn Ascending="true">
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
</OrderByColumn>
<OrderByColumn Ascending="true">
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
</OrderByColumn>
<OrderByColumn Ascending="true">
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
</OrderByColumn>
<OrderByColumn Ascending="true">
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OrderByColumn>
</OrderBy>
<RelOp AvgRowSize="94" EstimateCPU="75.5786" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="44400500" LogicalOp="Inner Join" NodeId="2" Parallel="false" PhysicalOp="Hash Match" EstimatedTotalSubtreeCost="93.6068">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<MemoryFractions Input="0.816955" Output="0.0120753" />
<Hash>
<DefinedValues />
<HashKeysBuild>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="NAMEID" />
</HashKeysBuild>
<HashKeysProbe>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
</HashKeysProbe>
<ProbeResidual>
<ScalarOperator ScalarString="[DC02001].[dbo].[TCUSDTL].[NAMEID] as [cd].[NAMEID]=[DC02001].[dbo].[TPOLACTD].[NAMEID] as [bd].[NAMEID]">
<Compare CompareOp="EQ">
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="NAMEID" />
</Identifier>
</ScalarOperator>
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
</Identifier>
</ScalarOperator>
</Compare>
</ScalarOperator>
</ProbeResidual>
<RelOp AvgRowSize="33" EstimateCPU="0.283312" EstimateIO="2.24609" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="257414" LogicalOp="Table Scan" NodeId="3" Parallel="false" PhysicalOp="Table Scan" EstimatedTotalSubtreeCost="2.5294" TableCardinality="257414">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="NAMEID" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
</OutputList>
<TableScan Ordered="false" ForcedIndex="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="NAMEID" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="ASSIGNEDPOLICY" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" Column="COMPANYPOLICYNUMBER" />
</DefinedValue>
</DefinedValues>
<Object Database="[DC02001]" Schema="[dbo]" Table="[TCUSDTL]" Alias="[cd]" IndexKind="Heap" Storage="RowStore" />
</TableScan>
</RelOp>
<RelOp AvgRowSize="86" EstimateCPU="7.96164" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="1405060" LogicalOp="Inner Join" NodeId="4" Parallel="false" PhysicalOp="Hash Match" EstimatedTotalSubtreeCost="15.4988">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<MemoryFractions Input="0.179818" Output="0.00265786" />
<Hash>
<DefinedValues />
<HashKeysBuild>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAMEID" />
</HashKeysBuild>
<HashKeysProbe>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
</HashKeysProbe>
<ProbeResidual>
<ScalarOperator ScalarString="[DC02001].[dbo].[SNAMES].[NAMEID] as [sn].[NAMEID]=[DC02001].[dbo].[TPOLACTD].[NAMEID] as [bd].[NAMEID]">
<Compare CompareOp="EQ">
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAMEID" />
</Identifier>
</ScalarOperator>
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
</Identifier>
</ScalarOperator>
</Compare>
</ScalarOperator>
</ProbeResidual>
<RelOp AvgRowSize="56" EstimateCPU="0.0416996" EstimateIO="0.221644" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="37766" LogicalOp="Index Scan" NodeId="5" Parallel="false" PhysicalOp="Index Scan" EstimatedTotalSubtreeCost="0.263343" TableCardinality="37766">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAMEID" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
</OutputList>
<IndexScan Ordered="false" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAMEID" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Alias="[sn]" Column="NAME" />
</DefinedValue>
</DefinedValues>
<Object Database="[DC02001]" Schema="[dbo]" Table="[SNAMES]" Index="[SNAMES_names]" Alias="[sn]" IndexKind="NonClustered" Storage="RowStore" />
</IndexScan>
</RelOp>
<RelOp AvgRowSize="46" EstimateCPU="4.94636" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="702122" LogicalOp="Inner Join" NodeId="6" Parallel="false" PhysicalOp="Hash Match" EstimatedTotalSubtreeCost="7.27381">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<MemoryFractions Input="0.00322675" Output="4.7694E-05" />
<Hash>
<DefinedValues />
<HashKeysBuild>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="COVERAGE" />
</HashKeysBuild>
<HashKeysProbe>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
</HashKeysProbe>
<ProbeResidual>
<ScalarOperator ScalarString="[DC02001].[dbo].[SCOVTBL].[COVERAGE] as [sd].[COVERAGE]=[DC02001].[dbo].[TPOLACTD].[COVERAGECODE] as [bd].[COVERAGECODE]">
<Compare CompareOp="EQ">
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="COVERAGE" />
</Identifier>
</ScalarOperator>
<ScalarOperator>
<Identifier>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
</Identifier>
</ScalarOperator>
</Compare>
</ScalarOperator>
</ProbeResidual>
<RelOp AvgRowSize="37" EstimateCPU="0.0001966" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="36" LogicalOp="Index Scan" NodeId="7" Parallel="false" PhysicalOp="Index Scan" EstimatedTotalSubtreeCost="0.0033216" TableCardinality="36">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="COVERAGE" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</OutputList>
<IndexScan Ordered="false" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="COVERAGE" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Alias="[sd]" Column="DESCRIPTION" />
</DefinedValue>
</DefinedValues>
<Object Database="[DC02001]" Schema="[dbo]" Table="[SCOVTBL]" Index="[SCOVTBL_coverage]" Alias="[sd]" IndexKind="NonClustered" Storage="RowStore" />
</IndexScan>
</RelOp>
<RelOp AvgRowSize="21" EstimateCPU="0.6973" EstimateIO="1.62683" EstimateRebinds="0" EstimateRewinds="0" EstimatedExecutionMode="Row" EstimateRows="633766" LogicalOp="Index Scan" NodeId="8" Parallel="false" PhysicalOp="Index Scan" EstimatedTotalSubtreeCost="2.32413" TableCardinality="633766">
<OutputList>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
</OutputList>
<IndexScan Ordered="false" ForcedIndex="false" ForceSeek="false" ForceScan="false" NoExpandHint="false" Storage="RowStore">
<DefinedValues>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="NAMEID" />
</DefinedValue>
<DefinedValue>
<ColumnReference Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Alias="[bd]" Column="COVERAGECODE" />
</DefinedValue>
</DefinedValues>
<Object Database="[DC02001]" Schema="[dbo]" Table="[TPOLACTD]" Index="[TPOLACTD_coverage]" Alias="[bd]" IndexKind="NonClustered" Storage="RowStore" />
</IndexScan>
</RelOp>
</Hash>
</RelOp>
</Hash>
</RelOp>
</Hash>
</RelOp>
</Sort>
</RelOp>
</Top>
</RelOp>
</QueryPlan>
</StmtSimple>
</Statements>
</Batch>
</BatchSequence>
</ShowPlanXML>