Question

今天我在我们的代码中发现了这个查询，它从我们的数据库中提取错误列表：

SELECT *
FROM   (
        SELECT Substring(title, 9, Patindex('%)%', title) - 9) AS SERVICE, *
        FROM   core.LOG
        WHERE  logtypeid = 1
               AND title LIKE 'Error: (%'
               AND lastmodified > '2010-06-21T00:00:00'
               AND lastmodified < '2010-06-22T00:00:00'
        ) serviceerrors
WHERE SERVICE = 'CheckHelpDeskEmail'

失败并出现以下错误：

传递给的无效长度参数 SUBSTRING功能。

如果我删除最后一行的WHERE子句，它可以正常工作。或者，如果我从内部子查询中取出WHERE子句并将其移动到主查询，它可以正常工作。所以这有效：

SELECT *
FROM   (
        SELECT Substring(title, 9, Patindex('%)%', title) - 9) AS SERVICE, *
        FROM   core.LOG
        ) serviceerrors
WHERE  logtypeid = 1
AND title LIKE 'Error: (%'
AND lastmodified > '2010-06-21T00:00:00'
AND lastmodified < '2010-06-22T00:00:00'
AND SERVICE = 'CheckHelpDeskEmail'

有谁知道为什么？我认为问题是SQL实际上是通过core.LOG表进行多次运行，并且它第一次只是在整个表上运行子串行而失败，因为某些行不会有'）'。但是，如果它运行WHERE子句中的其余行，则不会找到任何缺少'）'的行。然后它再次运行core.LOG表并运行其余的过滤器。这似乎是无效的，因为它将最终在数百万行上运行Substring函数，而在WHERE子句中的剩余过滤器中运行大约15行。

这是我的XML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="1.0" Build="9.00.3310.00" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
  <BatchSequence>
    <Batch>
      <Statements>
        <StmtSimple StatementCompId="1" StatementEstRows="1" StatementId="1" StatementOptmLevel="FULL" StatementSubTreeCost="36.4574" StatementText="SELECT *&#xD;&#xA;FROM   (&#xD;&#xA;       SELECT Substring(title, 9, Patindex('%)%', title) - 9) AS SERVICE,&#xD;&#xA;               *&#xD;&#xA;        FROM   core.LOG&#xD;&#xA;        WHERE  logtypeid = 1&#xD;&#xA;               AND title LIKE 'Error: (%'&#xD;&#xA;               AND lastmodified &gt; '2010-06-21T00:00:00'&#xD;&#xA;               AND lastmodified &lt; '2010-06-22T00:00:00'&#xD;&#xA;        ) serviceerrors&#xD;&#xA;WHERE SERVICE = 'CheckHelpDeskEmail'  &#xD;&#xA;" StatementType="SELECT">
          <StatementSetOptions ANSI_NULLS="false" ANSI_PADDING="false" ANSI_WARNINGS="false" ARITHABORT="true" CONCAT_NULL_YIELDS_NULL="false" NUMERIC_ROUNDABORT="false" QUOTED_IDENTIFIER="false" />
          <QueryPlan CachedPlanSize="47" CompileTime="10" CompileCPU="7" CompileMemory="544">
            <RelOp AvgRowSize="4544" EstimateCPU="1E-07" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Compute Scalar" NodeId="0" Parallel="false" PhysicalOp="Compute Scalar" EstimatedTotalSubtreeCost="36.4574">
              <OutputList>
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                <ColumnReference Column="Expr1003" />
              </OutputList>
              <ComputeScalar>
                <DefinedValues>
                  <DefinedValue>
                    <ColumnReference Column="Expr1003" />
                    <ScalarOperator ScalarString="substring([Aqueduct].[Core].[Log].[Title],(9),patindex(N'%)%',[Aqueduct].[Core].[Log].[Title])-(9))">
                      <Intrinsic FunctionName="substring">
                        <ScalarOperator>
                          <Identifier>
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                          </Identifier>
                        </ScalarOperator>
                        <ScalarOperator>
                          <Const ConstValue="(9)" />
                        </ScalarOperator>
                        <ScalarOperator>
                          <Arithmetic Operation="SUB">
                            <ScalarOperator>
                              <Intrinsic FunctionName="patindex">
                                <ScalarOperator>
                                  <Const ConstValue="N'%)%'" />
                                </ScalarOperator>
                                <ScalarOperator>
                                  <Identifier>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                  </Identifier>
                                </ScalarOperator>
                              </Intrinsic>
                            </ScalarOperator>
                            <ScalarOperator>
                              <Const ConstValue="(9)" />
                            </ScalarOperator>
                          </Arithmetic>
                        </ScalarOperator>
                      </Intrinsic>
                    </ScalarOperator>
                  </DefinedValue>
                </DefinedValues>
                <RelOp AvgRowSize="4342" EstimateCPU="0.0288036" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Gather Streams" NodeId="1" Parallel="true" PhysicalOp="Parallelism" EstimatedTotalSubtreeCost="36.4574">
                  <OutputList>
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                  </OutputList>
                  <Parallelism>
                    <RelOp AvgRowSize="4342" EstimateCPU="0.0128582" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="1" LogicalOp="Filter" NodeId="2" Parallel="true" PhysicalOp="Filter" EstimatedTotalSubtreeCost="36.4286">
                      <OutputList>
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                      </OutputList>
                      <Filter StartupExpression="false">
                        <RelOp AvgRowSize="4342" EstimateCPU="0.0235734" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="11279.1" LogicalOp="Inner Join" NodeId="3" Parallel="true" PhysicalOp="Nested Loops" EstimatedTotalSubtreeCost="36.4157">
                          <OutputList>
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                          </OutputList>
                          <NestedLoops Optimized="true" WithUnorderedPrefetch="true">
                            <OuterReferences>
                              <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                              <ColumnReference Column="Expr1004" />
                            </OuterReferences>
                            <RelOp AvgRowSize="19" EstimateCPU="0.00628203" EstimateIO="0.0186806" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="11279.1" LogicalOp="Index Seek" NodeId="6" Parallel="true" PhysicalOp="Index Seek" EstimatedTotalSubtreeCost="0.0249626">
                              <OutputList>
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                              </OutputList>
                              <IndexScan Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" NoExpandHint="false">
                                <DefinedValues>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                                  </DefinedValue>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                                  </DefinedValue>
                                </DefinedValues>
                                <Object Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Index="[IX_LastModified]" />
                                <SeekPredicates>
                                  <SeekPredicate>
                                    <StartRange ScanType="GT">
                                      <RangeColumns>
                                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                                      </RangeColumns>
                                      <RangeExpressions>
                                        <ScalarOperator ScalarString="'2010-06-21 00:00:00.000'">
                                          <Const ConstValue="'2010-06-21 00:00:00.000'" />
                                        </ScalarOperator>
                                      </RangeExpressions>
                                    </StartRange>
                                    <EndRange ScanType="LT">
                                      <RangeColumns>
                                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModified" />
                                      </RangeColumns>
                                      <RangeExpressions>
                                        <ScalarOperator ScalarString="'2010-06-22 00:00:00.000'">
                                          <Const ConstValue="'2010-06-22 00:00:00.000'" />
                                        </ScalarOperator>
                                      </RangeExpressions>
                                    </EndRange>
                                  </SeekPredicate>
                                </SeekPredicates>
                              </IndexScan>
                            </RelOp>
                            <RelOp AvgRowSize="4447" EstimateCPU="0.0001581" EstimateIO="0.003125" EstimateRebinds="11278.1" EstimateRewinds="0" EstimateRows="1" LogicalOp="Clustered Index Seek" NodeId="8" Parallel="true" PhysicalOp="Clustered Index Seek" EstimatedTotalSubtreeCost="36.3672">
                              <OutputList>
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                                <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                              </OutputList>
                              <IndexScan Lookup="true" Ordered="true" ScanDirection="FORWARD" ForcedIndex="false" NoExpandHint="false">
                                <DefinedValues>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                  </DefinedValue>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Details" />
                                  </DefinedValue>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="IdentifierHash" />
                                  </DefinedValue>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LastModifier" />
                                  </DefinedValue>
                                  <DefinedValue>
                                    <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                                  </DefinedValue>
                                </DefinedValues>
                                <Object Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Index="[PK_Core_Log]" TableReferenceId="-1" />
                                <SeekPredicates>
                                  <SeekPredicate>
                                    <Prefix ScanType="EQ">
                                      <RangeColumns>
                                        <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                                      </RangeColumns>
                                      <RangeExpressions>
                                        <ScalarOperator ScalarString="[Aqueduct].[Core].[Log].[LogId]">
                                          <Identifier>
                                            <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogId" />
                                          </Identifier>
                                        </ScalarOperator>
                                      </RangeExpressions>
                                    </Prefix>
                                  </SeekPredicate>
                                </SeekPredicates>
                              </IndexScan>
                            </RelOp>
                          </NestedLoops>
                        </RelOp>
                        <Predicate>
                          <ScalarOperator ScalarString="substring([Aqueduct].[Core].[Log].[Title],(9),patindex(N'%)%',[Aqueduct].[Core].[Log].[Title])-(9))=N'CheckHelpDeskEmail' AND [Aqueduct].[Core].[Log].[Title] like N'Error: (%' AND [Aqueduct].[Core].[Log].[LogTypeId]=(1)">
                            <Logical Operation="AND">
                              <ScalarOperator>
                                <Compare CompareOp="EQ">
                                  <ScalarOperator>
                                    <Intrinsic FunctionName="substring">
                                      <ScalarOperator>
                                        <Identifier>
                                          <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                        </Identifier>
                                      </ScalarOperator>
                                      <ScalarOperator>
                                        <Const ConstValue="(9)" />
                                      </ScalarOperator>
                                      <ScalarOperator>
                                        <Arithmetic Operation="SUB">
                                          <ScalarOperator>
                                            <Intrinsic FunctionName="patindex">
                                              <ScalarOperator>
                                                <Const ConstValue="N'%)%'" />
                                              </ScalarOperator>
                                              <ScalarOperator>
                                                <Identifier>
                                                  <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                                </Identifier>
                                              </ScalarOperator>
                                            </Intrinsic>
                                          </ScalarOperator>
                                          <ScalarOperator>
                                            <Const ConstValue="(9)" />
                                          </ScalarOperator>
                                        </Arithmetic>
                                      </ScalarOperator>
                                    </Intrinsic>
                                  </ScalarOperator>
                                  <ScalarOperator>
                                    <Const ConstValue="N'CheckHelpDeskEmail'" />
                                  </ScalarOperator>
                                </Compare>
                              </ScalarOperator>
                              <ScalarOperator>
                                <Intrinsic FunctionName="like">
                                  <ScalarOperator>
                                    <Identifier>
                                      <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="Title" />
                                    </Identifier>
                                  </ScalarOperator>
                                  <ScalarOperator>
                                    <Const ConstValue="N'Error: (%'" />
                                  </ScalarOperator>
                                </Intrinsic>
                              </ScalarOperator>
                              <ScalarOperator>
                                <Compare CompareOp="EQ">
                                  <ScalarOperator>
                                    <Identifier>
                                      <ColumnReference Database="[Aqueduct]" Schema="[Core]" Table="[Log]" Column="LogTypeId" />
                                    </Identifier>
                                  </ScalarOperator>
                                  <ScalarOperator>
                                    <Const ConstValue="(1)" />
                                  </ScalarOperator>
                                </Compare>
                              </ScalarOperator>
                            </Logical>
                          </ScalarOperator>
                        </Predicate>
                      </Filter>
                    </RelOp>
                  </Parallelism>
                </RelOp>
              </ComputeScalar>
            </RelOp>
          </QueryPlan>
        </StmtSimple>
      </Statements>
    </Batch>
  </BatchSequence>
</ShowPlanXML>

Answer 1

您的代码无效假设。在像SQL这样的声明性集合导向语言中，执行可以自由选择它认为合适的任何执行计划。您认为低效的内容很可能是有效的优化，其中标题首先从满足lastmodified上的谓词或类似内容的索引进行投影。你不能对执行顺序做任何假设，因此不允许你在投影列表中有像SUBSTRING（..，9，..）那样会在某些行上轰炸的表达式。

由类似的无效假设引起的问题的另一个例子是SQL Server boolean operator short-circuit评估错误。

在SQL Server 2005中对此查询执行的查询执行是什么？

1 个答案: