Sql 为什么CTE比Temp表慢?
我有一个简单的存储过程,其中有多个带有子句的Sql 为什么CTE比Temp表慢?,sql,sql-server,temp-tables,Sql,Sql Server,Temp Tables,我有一个简单的存储过程,其中有多个带有子句的 有些代码是这样的: WITH cteRowNums AS ( SELECT ROW_NUMBER() OVER(ORDER BY fcmp.EmpUserID, fcmp.WorkCellID, fcmp.ActivityTS) AS RowNumber, fcmp.ActivityTS, fcmp.ArtifactTypeID, fcmp.ServerDateID,
有些代码是这样的:
WITH cteRowNums AS
(
SELECT
ROW_NUMBER() OVER(ORDER BY fcmp.EmpUserID, fcmp.WorkCellID, fcmp.ActivityTS) AS RowNumber,
fcmp.ActivityTS,
fcmp.ArtifactTypeID,
fcmp.ServerDateID,
fcmp.ServerHourID,
fcmp.EmpUserID,
fcmp.WorkCellID
FROM dbo.FactCassetteMarkingProcessing fcmp
WHERE ServerDateID >= '2007-01-01'
),
-- Make an attempt at identifying what each user did in their "session" by self-joining
cteJoinCurAndNext AS
(
SELECT
[Current Row].ArtifactTypeID,
[Current Row].ServerDateID,
[Current Row].ServerHourID,
[Current Row].EmpUserID,
[Current Row].WorkCellID
FROM cteRowNums [Current Row]
LEFT OUTER JOIN cteRowNums [Next Row] ON [Next Row].RowNumber = [Current Row].RowNumber + 1
WHERE [Current Row].ArtifactTypeID = 2
OR ([Current Row].ArtifactTypeID = 1 AND [Next Row].ArtifactTypeID = 2
AND [Current Row].EmpUserID = [Next Row].EmpUserID
AND [Current Row].WorkCellID = [Next Row].WorkCellID)
),
-- Do some aggregations
cteAggregates AS
(
SELECT
EmpUserID,
ServerDateID,
ServerHourID,
COUNT(NULLIF(ArtifactTypeID, 2)) AS SpecimensProcessedCount,
COUNT(NULLIF(ArtifactTypeID, 1)) AS BlocksProcessedCount
FROM cteJoinCurAndNext
GROUP BY EmpUserID, ServerDateID, ServerHourID
)
SELECT * FROM cteAggregates
问题是大约250万行需要花费大量时间。我在40分钟时取消了执行查询
如果我用temporary
表更改这段代码,执行速度会快得多。是否有任何方法可以仅使用CTE获得几乎相同的性能?有两个原因
可能更重要的原因是SQLServer没有实现CTE。因此,对于每个引用,SQL Server都会重新计算整个CTE。据我所知,SQL Server也不会对执行DAG执行常见的子查询优化,因此它总是重新生成CTE(尽管每个实例的执行计划可能不同)
第二个原因是临时表具有统计信息,这些统计信息可以通知查询计划创建更好的计划
我想你可以简化逻辑。但是,您需要提出一个新问题,解释您想要做什么,以及样本数据和期望的结果