Sql 使用子查询与字符串进行联接的查询时间

我有这样一个问题：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
     AND t2.time IN (SELECT year FROM activeYears WHERE active = 1)

其中activeYears.year为NVARCHAR50，则每年为一行

为什么该联接的运行时间比此查询快：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id AND t2.time IN ('2009','2010')

这是一个简短的版本，基本上我有一个使用子查询的带有连接的大型查询。当我将子查询更改为字符串进行测试时，运行时间会增加一倍，即使在清除缓存时也是如此。我认为这可能是一个强制转换问题，但我也尝试将两个变量声明为NVARCHAR50，并在查询中使用它们，结果没有什么不同

这让我困惑了几天，我不明白为什么子查询速度更快，除非查询实际上是以不同的方式构建的

谢谢

编辑-执行计划信息 我区分了两个执行计划，并将尝试给你匿名的亮点

执行计划的MissingIndexes部分用于更快的子查询：

         <QueryPlan CachedPlanSize="196" CompileTime="2166" CompileCPU="2166" CompileMemory="18640">
            <MissingIndexes>
             <MissingIndexGroup Impact="41.4663">
                <MissingIndex Database="[database]" Schema="[dbo]" Table="[table2]">
                 <ColumnGroup Usage="EQUALITY">
                   <Column Name="[time]" ColumnId="3" />
                    <Column Name="[id]" ColumnId="10" />
                  </ColumnGroup>
                </MissingIndex>
              </MissingIndexGroup>
            </MissingIndexes>

然后串

Table 'table2'. Scan count 1, logical reads 2339848, physical reads 0, read-ahead reads 2303, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table3'. Scan count 1016, logical reads 4467, physical reads 21, read-ahead reads 1047, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 659, logical reads 5863, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table4'. Scan count 1, logical reads 126, physical reads 0, read-ahead reads 126, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table1'. Scan count 1033, logical reads 5228, physical reads 60, read-ahead reads 120, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table5'. Scan count 1, logical reads 219, physical reads 0, read-ahead reads 219, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'activeYear'. Scan count 1, logical reads 2, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table6'. Scan count 1, logical reads 2, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 16719 ms,  elapsed time = 17447 ms.

这个连接中的表比简化查询中的多几个，但我关心的只是单个连接上的字符串与子查询的变化。。。希望这是独立的，因为t1单独连接到这个查询中的所有表。

---

猜测：中的第一个查询已转换为联接：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
JOIN activeYears ay ON t2.time = ay.year 
WHERE ay.active = 1

当二维查询的中转换为或甚至联合时：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
WHERE t2.time = '2009'
   OR t2.time = '2010'

---

推测：中的第一个查询已转换为联接：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
JOIN activeYears ay ON t2.time = ay.year 
WHERE ay.active = 1

当二维查询的中转换为或甚至联合时：

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
WHERE t2.time = '2009'
   OR t2.time = '2010'

---

你比较过计划了吗？您是否在“设置统计信息IO”和“设置统计信息时间”的情况下进行了测试？我猜第二种方法会欺骗查询优化器，让它从t2开始。时间会让它变小。第一个看起来像是从t1开始，然后连接到t2，因为在子查询中通常更昂贵。可能有很多原因，请检查查询计划以获得提示。一种猜测是前者可以使用后者不能使用的索引。如果执行，您会得到什么：从表1 t1选择*在t1.id=t2.id上连接表2 t2，其中t2.time在'2009'，'2010'@Mitch中，这样做要快得多。事实上，当我这样做的时候，它会反转。在'2009'和'2010'中放置t2.time的位置成本稍高，但运行速度更快。在active=1的activeYears中放置所选年份中的t2.time的成本稍低，但返回结果的速度也较慢。@Richard I按照您的建议添加了一些统计信息。我不确定工作台是什么，但它似乎是最大的区别，除非我遗漏了更重要的东西？你比较过计划了吗？您是否在“设置统计信息IO”和“设置统计信息时间”的情况下进行了测试？我猜第二种方法会欺骗查询优化器，让它从t2开始。时间会让它变小。第一个看起来像是从t1开始，然后连接到t2，因为在子查询中通常更昂贵。可能有很多原因，请检查查询计划以获得提示。一种猜测是前者可以使用后者不能使用的索引。如果执行，您会得到什么：从表1 t1选择*在t1.id=t2.id上连接表2 t2，其中t2.time在'2009'，'2010'@Mitch中，这样做要快得多。事实上，当我这样做的时候，它会反转。在'2009'和'2010'中放置t2.time的位置成本稍高，但运行速度更快。在active=1的activeYears中放置所选年份中的t2.time的成本稍低，但返回结果的速度也较慢。@Richard I按照您的建议添加了一些统计信息。我不确定worktable是什么，但它似乎是最大的区别，除非我遗漏了更重要的东西？考虑到那些ScalarOperator标记，这是有意义的，我看到了OR的使用。但在更快的查询中，它表示[t2].[time]=N'2009'和[t2].[time]=N'2010'。。。它不可能知道这是那里仅有的两个可能的值，我只能假设它正在使用一个索引来知道这两个nvarchar之间没有会被错误的查询获取的值？我可能会得出这样的结论：它只知道在2009年和2010年之间没有什么，但实际的字段与此略有不同，甚至没有数字。更像是1982-1985年和1986-2000年。考虑到那些ScalarOperator标签，这是有意义的，我看到使用了OR。但在更快的查询中，它表示[t2].[time]=N'2009'和[t2].[time]=N'2010'。。。它不可能知道这是那里仅有的两个可能的值，我只能假设它正在使用一个索引来知道这两个nvarchar之间没有会被错误的查询获取的值？我可能会得出这样的结论：它只知道在2009年和2010年之间没有什么，但实际的字段与此略有不同，甚至没有数字。更像1982-1985年和1986-2000年。

Table 'activeYear'. Scan count 2, logical reads 2010, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table2'. Scan count 1, logical reads 2339848, physical reads 0, read-ahead reads 2303, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table3'. Scan count 1016, logical reads 4624, physical reads 21, read-ahead reads 1047, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 12, logical reads 109, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table4'. Scan count 1, logical reads 126, physical reads 0, read-ahead reads 126, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table1'. Scan count 1033, logical reads 5331, physical reads 57, read-ahead reads 123, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table5'. Scan count 1, logical reads 219, physical reads 0, read-ahead reads 219, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table6'. Scan count 1, logical reads 2, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 10328 ms,  elapsed time = 11479 ms.

Table 'table2'. Scan count 1, logical reads 2339848, physical reads 0, read-ahead reads 2303, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table3'. Scan count 1016, logical reads 4467, physical reads 21, read-ahead reads 1047, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Worktable'. Scan count 659, logical reads 5863, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table4'. Scan count 1, logical reads 126, physical reads 0, read-ahead reads 126, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table1'. Scan count 1033, logical reads 5228, physical reads 60, read-ahead reads 120, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table5'. Scan count 1, logical reads 219, physical reads 0, read-ahead reads 219, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'activeYear'. Scan count 1, logical reads 2, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'table6'. Scan count 1, logical reads 2, physical reads 2, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 16719 ms,  elapsed time = 17447 ms.

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
JOIN activeYears ay ON t2.time = ay.year 
WHERE ay.active = 1

SELECT * FROM table1 t1
JOIN table2 t2 ON t1.id = t2.id 
WHERE t2.time = '2009'
   OR t2.time = '2010'