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INNER JOIN和锁定

sql-serverlockinginner-join
5

我有两个表TableA和TableB，它们含有我想要同时检索和更新的信息。当我使用

SELECT TOP 2 SomeFieldA
FROM TableA WITH (ROWLOCK , UPDLOCK , READPAST)

一切都正常，进程1看到第1行和第2行，进程2看到第3行和第4行，这是期望的行为。当我执行EXEC sp_lock时，只看到两个KEY条目。但是，当我将语句更改为

SELECT TOP 2 SomeFieldA
FROM TableA WITH (ROWLOCK , UPDLOCK , READPAST)
INNER JOIN
Table B WITH ( ROWLOCK , UPDLOCK , READPAST )
ON TableA.ID = TableB.IDRef`

第一个进程看到了第1行和第2行，但第2个进程什么也没看到。执行sp_lock命令显示现在所有的行都被阻塞了。为什么会出现这种情况？

编辑：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="1.1" Build="10.50.1617.0" xmlns="http://schemas.microsoft.com/sqlserver/2004/07/showplan">
  <BatchSequence>
    <Batch>
      <Statements>
        <StmtSimple StatementCompId="2" StatementEstRows="2" StatementId="1" StatementOptmLevel="FULL" StatementOptmEarlyAbortReason="GoodEnoughPlanFound" StatementSubTreeCost="0.00670141" StatementText="SELECT TOP 2 * FROM Request R WITH ( ROWLOCK , UPDLOCK , READPAST) INNER JOIN Options O WITH ( ROWLOCK , UPDLOCK , READPAST ) ON (R.RequestID = O.RequestID)&#xD;&#xA;&#xD;" StatementType="SELECT" QueryHash="0xA35BE09F9DD52334" QueryPlanHash="0x95BEDE8C14AB4C68">
          <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" CachedPlanSize="16" CompileTime="3" CompileCPU="3" CompileMemory="160">
            <RelOp AvgRowSize="58" EstimateCPU="2E-07" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="2" LogicalOp="Top" NodeId="0" Parallel="false" PhysicalOp="Top" EstimatedTotalSubtreeCost="0.00670141">
              <OutputList>
                <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="RequestID" />
                <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="DateEntered" />
                <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="Priority" />
                <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="RequestID" />
                <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="SomeOptions" />
              </OutputList>
              <RunTimeInformation>
                <RunTimeCountersPerThread Thread="0" ActualRows="2" ActualEndOfScans="1" ActualExecutions="1" />
              </RunTimeInformation>
              <Top RowCount="false" IsPercent="false" WithTies="false">
                <TopExpression>
                  <ScalarOperator ScalarString="(2)">
                    <Const ConstValue="(2)" />
                  </ScalarOperator>
                </TopExpression>
                <RelOp AvgRowSize="58" EstimateCPU="7.524E-05" EstimateIO="0" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="2" LogicalOp="Inner Join" NodeId="1" Parallel="false" PhysicalOp="Nested Loops" EstimatedTotalSubtreeCost="0.00670121">
                  <OutputList>
                    <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="RequestID" />
                    <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="DateEntered" />
                    <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="Priority" />
                    <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="RequestID" />
                    <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="SomeOptions" />
                  </OutputList>
                  <RunTimeInformation>
                    <RunTimeCountersPerThread Thread="0" ActualRows="2" ActualEndOfScans="0" ActualExecutions="1" />
                  </RunTimeInformation>
                  <NestedLoops Optimized="false">
                    <Predicate>
                      <ScalarOperator ScalarString="[TestDatabase].[dbo].[Options].[RequestID] as [O].[RequestID]=[TestDatabase].[dbo].[Request].[RequestID] as [R].[RequestID]">
                        <Compare CompareOp="EQ">
                          <ScalarOperator>
                            <Identifier>
                              <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="RequestID" />
                            </Identifier>
                          </ScalarOperator>
                          <ScalarOperator>
                            <Identifier>
                              <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="RequestID" />
                            </Identifier>
                          </ScalarOperator>
                        </Compare>
                      </ScalarOperator>
                    </Predicate>
                    <RelOp AvgRowSize="45" EstimateCPU="0.0001603" EstimateIO="0.003125" EstimateRebinds="0" EstimateRewinds="0" EstimateRows="2" LogicalOp="Clustered Index Scan" NodeId="2" Parallel="false" PhysicalOp="Clustered Index Scan" EstimatedTotalSubtreeCost="0.0032842" TableCardinality="3">
                      <OutputList>
                        <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="RequestID" />
                        <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="SomeOptions" />
                      </OutputList>
                      <RunTimeInformation>
                        <RunTimeCountersPerThread Thread="0" ActualRows="2" ActualEndOfScans="0" ActualExecutions="1" />
                      </RunTimeInformation>
                      <IndexScan Ordered="false" ForcedIndex="false" NoExpandHint="false">
                        <DefinedValues>
                          <DefinedValue>
                            <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="RequestID" />
                          </DefinedValue>
                          <DefinedValue>
                            <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Alias="[O]" Column="SomeOptions" />
                          </DefinedValue>
                        </DefinedValues>
                        <Object Database="[TestDatabase]" Schema="[dbo]" Table="[Options]" Index="[PK__Options__33A8519A1DE57479]" Alias="[O]" IndexKind="Clustered" />
                      </IndexScan>
                    </RelOp>
                    <RelOp AvgRowSize="20" EstimateCPU="8.51E-05" EstimateIO="0.0032035" EstimateRebinds="0" EstimateRewinds="1.33333" EstimateRows="6" LogicalOp="Table Scan" NodeId="3" Parallel="false" PhysicalOp="Table Scan" EstimatedTotalSubtreeCost="0.00340207" TableCardinality="6">
                      <OutputList>
                        <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="RequestID" />
                        <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="DateEntered" />
                        <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="Priority" />
                      </OutputList>
                      <RunTimeInformation>
                        <RunTimeCountersPerThread Thread="0" ActualRows="8" ActualEndOfScans="1" ActualExecutions="2" />
                      </RunTimeInformation>
                      <TableScan Ordered="false" ForcedIndex="false" NoExpandHint="false">
                        <DefinedValues>
                          <DefinedValue>
                            <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="RequestID" />
                          </DefinedValue>
                          <DefinedValue>
                            <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="DateEntered" />
                          </DefinedValue>
                          <DefinedValue>
                            <ColumnReference Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" Column="Priority" />
                          </DefinedValue>
                        </DefinedValues>
                        <Object Database="[TestDatabase]" Schema="[dbo]" Table="[Request]" Alias="[R]" IndexKind="Heap" />
                      </TableScan>
                    </RelOp>
                  </NestedLoops>
                </RelOp>
              </Top>
            </RelOp>
          </QueryPlan>
        </StmtSimple>
      </Statements>
    </Batch>
  </BatchSequence>
</ShowPlanXML>

SQL:

CREATE TABLE Request
(
    RequestID   INT PRIMARY KEY,
    Priority    INT,
    DateEntered DATETIME
)

CREATE TABLE Options
(
    RequestIDRef    INT PRIMARY KEY,
    SomeOptions     NVARCHAR(MAX)
)
ALTER TABLE Options ADD

    CONSTRAINT FK_REQUESTIDREF FOREIGN KEY ( RequestIDRef ) REFERENCES [Request] ( RequestID )

GO

INSERT INTO Request VALUES ( 1, 2, GETDATE() )
INSERT INTO Request VALUES ( 2, 1, GETDATE() )
INSERT INTO Request VALUES ( 3, 3, GETDATE() )
INSERT INTO Request VALUES ( 4, 2, GETDATE() )

INSERT INTO Options VALUES ( 1, 'a' )
INSERT INTO Options VALUES ( 2, 'b' )
INSERT INTO Options VALUES ( 3, 'c' )
INSERT INTO Options VALUES ( 4, 'd' )

CREATE NONCLUSTERED INDEX IX_REQUESTIDREF ON [Options] ( RequestIDRef )
CREATE NONCLUSTERED INDEX IX_PRIORITY_DATEENTERED ON [Request] ( Priority , DateEntered ) INCLUDE ( RequestID )

现在

，
BEGIN TRANSACTION

SELECT TOP 2 * FROM [Request] WITH ( ROWLOCK , UPDLOCK , READPAST ) INNER JOIN [Options] WITH ( ROWLOCK , UPDLOCK , READPAST ) ON ( Request.RequestID = Options.RequestIDRef ) ORDER BY Priority, DateEntered

WAITFOR DELAY '00:00:02.5'

COMMIT TRANSACTION

在Query1中，返回了2和1，符合预期，但是在Query2中没有返回任何结果。然而，如果我移除INNER JOIN和第二个表格，它就可以工作，并在Query1中返回(2,1)，在Query2中返回(3,4)。

每个表中有多少行？ - Damien_The_Unbeliever
请问您能否添加查询计划、实际数据和索引吗？ - gbn
返回只翻译文本，不要使用XML。 - gbn
1个回答
4
逻辑上，A和B的笛卡尔积仅限于交集或匹配行。要找到这些匹配行，需要查看TableA.ID和TableB.IDRef。如果没有索引，则至少需要在其中一个表上进行表扫描。因此，所有行都将被锁定以进行扫描。
因此，TableA.ID和TableB.IDRef都需要有索引。我怀疑TableA.ID已经作为PK拥有索引，但TableB.IDRef没有。
顺便说一句，TOP是后来应用的。
这类似于我在ORDER BY and WITH(ROWLOCK, UPDLOCK, READPAST)中回答的情况，其中有没有ORDER BY和没有索引的TOP：如果将ORDER BY添加到第一个查询中，那么第二个进程很可能也看不到任何内容。
编辑：对于您的更新，SELECT *将使索引无效并导致扫描：SELECT *不太有用，因为它们不是覆盖索引。
嗨gbn，再次感谢。但还是无法工作。请注意我的编辑。 - SQL Learner
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