我有两个表TableA和TableB，它们包含我想要检索和同时更新的信息。当我使用
SELECT TOP 2 SomeFieldA
FROM TableA WITH (ROWLOCK , UPDLOCK , READPAST)
一切正常，Process 1看到第1行和第2行，而Process 2看到第3行和第4行。这是预期的行为。此外，当我执行EXEC sp_lock时，我只看到两个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`
第一个进程看到第1行和第2行，但进程2看不到任何内容。执行sp_lock表示现在所有行都被阻止了。为什么会这样？
修改：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)

" 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
按预期返回2和1，但在Query2上它不返回任何内容。但是，如果我删除它INNER JOIN和第二个表，它将在Query1中返回（2,1），在Query2中返回（3,4）。
答案 0 :(得分：4)
逻辑上，A和B的笛卡尔乘积仅限于交点或匹配行。
要查找这些匹配的行，请查看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，所有行都被锁定以进行扫描
因此TableA.ID和TableB.IDRef都需要索引。我怀疑TableA.ID已经具有PK但是TableB.IDRef没有。
TOP后来应用BTW
这与我的答案类似，其中TOP没有ORDER BY且没有索引：ORDER BY and WITH(ROWLOCK, UPDLOCK, READPAST)。如果您将ORDER BY添加到第一个查询，那么第二个进程将不会看到太多可能的任何内容。
编辑：对于您的更新，SELECT *将使索引使用无效并导致扫描：索引与SELECT *没有太大用处，因为它们没有覆盖