SQL 慢速 UDF 的替代方案
SQL Alternatives to Slow UDF
带有两个 UDT 参数的查询需要 0.3 秒，但是当封装在一个内联 table 值函数中时，它需要 3.5+ 秒。
我已经阅读了 (Why is a UDF so much slower than a subquery?)，但我正在努力学习如何 fix/rewrite。
根据@JasonALong 下面的反馈，
SELECT 语句的执行计划在 0.3 秒内完成：https://www.brentozar.com/pastetheplan/?id=HJnrqC53Z（请注意 SQL 在此页面上可用）。
下面粘贴了在 3.5 秒内完成的函数代码和执行计划 link：https://www.brentozar.com/pastetheplan/?id=BJZbqR93b
SELECT
SelectedContracts.MeasurableID,
SelectedContracts.EntityID,
EntityName,
EntityAbbrev,
EntityLogoURL,
EntityHex1,
EntityHex2,
EntitySportID,
MeasurableName,
MeasurableOrganizationID,
YearFilter,
SeasonFilter,
CategoryFilter,
ResultFilter,
Logo4Result,
MeasurableSportID,
MouseoverFooter,
ContractRank4Org,
ContractEndUTC,
HighContractPrice4Period,
HighTradeID,
HighTradeUTC,
HighTradeNumberOfContracts,
HighTradeCurrency,
LowContractPrice4Period,
LowTradeID,
LowTradeUTC,
LowTradeNumberOfContracts,
LowTradeCurrency,
LastTradePrice,
LastTradeID,
LastTradeUTC,
LastTradeNumberOfContracts,
LastTradeCurrency,
SecondLastTradePrice,
SecondLastTradeID,
SecondLastTradeUTC,
SecondLastTradeNumberOfContracts,
SecondLastTradeCurrency,
ContractPrice4ChangeCalc,
ContractID4ChangeCalc,
ContractUTC4ChangeCalc,
ContractsNumberTraded4ChangeCalc,
ContractCurrency4ChangeCalc,
HighestBidID,
HighestBidMemberID,
HighestBidPrice,
HighestBidAvailableContracts,
HighestBidCurrency,
LowestAskID,
LowestAskMemberID,
LowestAskPrice,
LowestAskAvailableContracts,
LowestAskCurrency
FROM
(
SELECT
dbo.Contracts.MeasurableID,
dbo.Contracts.EntityID
FROM
dbo.Contracts
WHERE
dbo.Contracts.MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
GROUP BY
dbo.Contracts.MeasurableID,
dbo.Contracts.EntityID
) SelectedContracts
INNER JOIN
(
SELECT
dbo.Entities.ID,
--dbo.Entities.OrganizationID, -- Get OrganizationID from Measurable since some Entities (European soccer teams) have multiple Orgs
dbo.Entities.EntityName,
dbo.Entities.EntityAbbrev,
dbo.Entities.logoURL AS EntityLogoURL,
dbo.Entities.Hex1 AS EntityHex1,
dbo.Entities.Hex2 AS EntityHex2,
dbo.Entities.SportID AS EntitySportID
FROM
dbo.Entities
) SelectedEntities ON SelectedContracts.EntityID = SelectedEntities.ID
INNER JOIN
(
SELECT
dbo.Measurables.ID AS MeasurableID,
dbo.Measurables.Name AS MeasurableName,
dbo.Measurables.OrganizationID AS MeasurableOrganizationID,
dbo.Measurables.[Year] AS YearFilter,
dbo.Measurables.Season AS SeasonFilter,
dbo.Measurables.Category AS CategoryFilter,
dbo.Measurables.Result AS ResultFilter,
dbo.Measurables.Logo4Result,
dbo.Measurables.SportID AS MeasurableSportID,
dbo.Measurables.MouseoverFooter,
dbo.Measurables.ContractRank4Org,
dbo.Measurables.EndUTC AS ContractEndUTC
FROM
dbo.Measurables
) MEASURABLES_table ON SelectedContracts.MeasurableID = MEASURABLES_table.MeasurableID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS HighContractPrice4Period,
ID AS HighTradeID,
UTCMatched AS HighTradeUTC,
NumberOfContracts AS HighTradeNumberOfContracts,
CurrencyCode AS HighTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ContractPrice DESC,
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND dbo.Contracts.UTCmatched < DATEADD(DAY, -30, SYSDATETIME())
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4HighTrade
WHERE
InnerSelect4HighTrade.RowNumber = 1
) HighTrades ON SelectedContracts.MeasurableID = HighTrades.MeasurableID AND SelectedContracts.EntityID = HighTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS LowContractPrice4Period,
ID AS LowTradeID,
UTCMatched AS LowTradeUTC,
NumberOfContracts AS LowTradeNumberOfContracts,
CurrencyCode AS LowTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ContractPrice ASC,
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND dbo.Contracts.UTCmatched < DATEADD(DAY, -30, SYSDATETIME())
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4LowTrade
WHERE InnerSelect4LowTrade.RowNumber = 1
) LowTrades ON SelectedContracts.MeasurableID = LowTrades.MeasurableID AND SelectedContracts.EntityID = LowTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS LastTradePrice,
ID AS LastTradeID,
UTCMatched AS LastTradeUTC,
NumberOfContracts AS LastTradeNumberOfContracts,
CurrencyCode AS LastTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4LastTrade
WHERE InnerSelect4LastTrade.RowNumber = 1
) LastTrades ON SelectedContracts.MeasurableID = LastTrades.MeasurableID AND SelectedContracts.EntityID = LastTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS SecondLastTradePrice,
ID AS SecondLastTradeID,
UTCMatched AS SecondLastTradeUTC,
NumberOfContracts AS SecondLastTradeNumberOfContracts,
CurrencyCode AS SecondLastTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
--need time filter???
) AS InnerSelect4SecondToLastTrade
WHERE InnerSelect4SecondToLastTrade.RowNumber = 2
) SecondToLastTrade ON SelectedContracts.MeasurableID = SecondToLastTrade.MeasurableID AND SelectedContracts.EntityID = SecondToLastTrade.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS ContractPrice4ChangeCalc,
ID AS ContractID4ChangeCalc,
UTCMatched AS ContractUTC4ChangeCalc,
NumberOfContracts AS ContractsNumberTraded4ChangeCalc,
CurrencyCode AS ContractCurrency4ChangeCalc
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC -- ID DESC equals the most recent trade if ties
) RowNumber
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
AND dbo.Contracts.UTCmatched < DATEADD(Day ,-30, SYSDATETIME())
) AS InnerSelect4ChangeCalcPerPeriod
WHERE InnerSelect4ChangeCalcPerPeriod.RowNumber = 1
) Trade4ChangeCalcPerPeriod ON SelectedContracts.MeasurableID = Trade4ChangeCalcPerPeriod.MeasurableID AND SelectedContracts.EntityID = Trade4ChangeCalcPerPeriod.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ID AS HighestBidID,
MemberID AS HighestBidMemberID,
BidPrice AS HighestBidPrice,
AvailableContracts AS HighestBidAvailableContracts,
CurrencyCode AS HighestBidCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
BidPrice DESC,
ID DESC
) RowNumber
FROM
dbo.Interest2Buy
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND AvailableContracts > 0
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4HighestBid
WHERE InnerSelect4HighestBid.RowNumber = 1
) HighestBids ON SelectedContracts.MeasurableID = HighestBids.MeasurableID AND SelectedContracts.EntityID = HighestBids.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ID AS LowestAskID,
MemberID AS LowestAskMemberID,
AskPrice AS LowestAskPrice,
AvailableContracts AS LowestAskAvailableContracts,
CurrencyCode AS LowestAskCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
AskPrice ASC,
ID DESC
) RowNumber
FROM
dbo.Interest2Sell
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND AvailableContracts > 0
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4BestAsk
WHERE InnerSelect4BestAsk.RowNumber = 1
) BestAsks ON SelectedContracts.MeasurableID = BestAsks.MeasurableID AND SelectedContracts.EntityID = BestAsks.EntityID
正如您在问题中提到的，标量函数和多语句 table 值函数 (mTVF) 都是 "black boxes" 优化器...
所以，我的问题是 "why is this so bad?"。答案是，为了想出一个尽可能高效执行的好计划，它需要了解有关特定要求的某些细节以及有关它将从中提取数据的 tables 的信息（这就是为什么过时的静态也会严重影响性能的原因）。所以...当您使用标量函数或 mTVF 时，优化器无法像使用内联代码那样评估所有需求。它的反应是简单地假设该函数只会执行一次并根据该假设制定计划。
由于假设是错误的，因此生成了错误的计划，最终导致糟糕的表现。
解决方案是重写有问题的函数...关键是#1，确保将它们重写为 "inline table valued functions" (iTVF)。这些是优化器将看到的唯一函数，就好像它们的代码直接输入到外部查询中一样（因此术语 "inline"）。如果您不熟悉 iTVF，它们有 2 个要求……1 它们必须是 table 函数（无论出于何种原因，MS STILL 还没有可用的标量版本）……以及…… 2 这是大问题...函数体必须是单个语句。
那么，如果您不需要 table 值函数，您需要标量函数怎么办？好吧，没有什么说多值函数不能 return 单个（标量）值......这就是为什么那些知道这种情况的人将他们的所有函数都编码为 iTVF。
好在网络上不乏关于创建 "inline scalar functions" 的信息，使用编码为 return 标量值的 table 函数。
希望这对您有所帮助...
使用连接代替 "IN" 子句帮助很大。 （尽管我还将 table var 更改为临时变量 table，这也有很大帮助。）
带有两个 UDT 参数的查询需要 0.3 秒，但是当封装在一个内联 table 值函数中时，它需要 3.5+ 秒。
我已经阅读了 (Why is a UDF so much slower than a subquery?)，但我正在努力学习如何 fix/rewrite。
根据@JasonALong 下面的反馈，
SELECT 语句的执行计划在 0.3 秒内完成：https://www.brentozar.com/pastetheplan/?id=HJnrqC53Z（请注意 SQL 在此页面上可用）。
下面粘贴了在 3.5 秒内完成的函数代码和执行计划 link：https://www.brentozar.com/pastetheplan/?id=BJZbqR93b
SELECT
SelectedContracts.MeasurableID,
SelectedContracts.EntityID,
EntityName,
EntityAbbrev,
EntityLogoURL,
EntityHex1,
EntityHex2,
EntitySportID,
MeasurableName,
MeasurableOrganizationID,
YearFilter,
SeasonFilter,
CategoryFilter,
ResultFilter,
Logo4Result,
MeasurableSportID,
MouseoverFooter,
ContractRank4Org,
ContractEndUTC,
HighContractPrice4Period,
HighTradeID,
HighTradeUTC,
HighTradeNumberOfContracts,
HighTradeCurrency,
LowContractPrice4Period,
LowTradeID,
LowTradeUTC,
LowTradeNumberOfContracts,
LowTradeCurrency,
LastTradePrice,
LastTradeID,
LastTradeUTC,
LastTradeNumberOfContracts,
LastTradeCurrency,
SecondLastTradePrice,
SecondLastTradeID,
SecondLastTradeUTC,
SecondLastTradeNumberOfContracts,
SecondLastTradeCurrency,
ContractPrice4ChangeCalc,
ContractID4ChangeCalc,
ContractUTC4ChangeCalc,
ContractsNumberTraded4ChangeCalc,
ContractCurrency4ChangeCalc,
HighestBidID,
HighestBidMemberID,
HighestBidPrice,
HighestBidAvailableContracts,
HighestBidCurrency,
LowestAskID,
LowestAskMemberID,
LowestAskPrice,
LowestAskAvailableContracts,
LowestAskCurrency
FROM
(
SELECT
dbo.Contracts.MeasurableID,
dbo.Contracts.EntityID
FROM
dbo.Contracts
WHERE
dbo.Contracts.MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
GROUP BY
dbo.Contracts.MeasurableID,
dbo.Contracts.EntityID
) SelectedContracts
INNER JOIN
(
SELECT
dbo.Entities.ID,
--dbo.Entities.OrganizationID, -- Get OrganizationID from Measurable since some Entities (European soccer teams) have multiple Orgs
dbo.Entities.EntityName,
dbo.Entities.EntityAbbrev,
dbo.Entities.logoURL AS EntityLogoURL,
dbo.Entities.Hex1 AS EntityHex1,
dbo.Entities.Hex2 AS EntityHex2,
dbo.Entities.SportID AS EntitySportID
FROM
dbo.Entities
) SelectedEntities ON SelectedContracts.EntityID = SelectedEntities.ID
INNER JOIN
(
SELECT
dbo.Measurables.ID AS MeasurableID,
dbo.Measurables.Name AS MeasurableName,
dbo.Measurables.OrganizationID AS MeasurableOrganizationID,
dbo.Measurables.[Year] AS YearFilter,
dbo.Measurables.Season AS SeasonFilter,
dbo.Measurables.Category AS CategoryFilter,
dbo.Measurables.Result AS ResultFilter,
dbo.Measurables.Logo4Result,
dbo.Measurables.SportID AS MeasurableSportID,
dbo.Measurables.MouseoverFooter,
dbo.Measurables.ContractRank4Org,
dbo.Measurables.EndUTC AS ContractEndUTC
FROM
dbo.Measurables
) MEASURABLES_table ON SelectedContracts.MeasurableID = MEASURABLES_table.MeasurableID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS HighContractPrice4Period,
ID AS HighTradeID,
UTCMatched AS HighTradeUTC,
NumberOfContracts AS HighTradeNumberOfContracts,
CurrencyCode AS HighTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ContractPrice DESC,
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND dbo.Contracts.UTCmatched < DATEADD(DAY, -30, SYSDATETIME())
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4HighTrade
WHERE
InnerSelect4HighTrade.RowNumber = 1
) HighTrades ON SelectedContracts.MeasurableID = HighTrades.MeasurableID AND SelectedContracts.EntityID = HighTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS LowContractPrice4Period,
ID AS LowTradeID,
UTCMatched AS LowTradeUTC,
NumberOfContracts AS LowTradeNumberOfContracts,
CurrencyCode AS LowTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ContractPrice ASC,
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND dbo.Contracts.UTCmatched < DATEADD(DAY, -30, SYSDATETIME())
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4LowTrade
WHERE InnerSelect4LowTrade.RowNumber = 1
) LowTrades ON SelectedContracts.MeasurableID = LowTrades.MeasurableID AND SelectedContracts.EntityID = LowTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS LastTradePrice,
ID AS LastTradeID,
UTCMatched AS LastTradeUTC,
NumberOfContracts AS LastTradeNumberOfContracts,
CurrencyCode AS LastTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4LastTrade
WHERE InnerSelect4LastTrade.RowNumber = 1
) LastTrades ON SelectedContracts.MeasurableID = LastTrades.MeasurableID AND SelectedContracts.EntityID = LastTrades.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS SecondLastTradePrice,
ID AS SecondLastTradeID,
UTCMatched AS SecondLastTradeUTC,
NumberOfContracts AS SecondLastTradeNumberOfContracts,
CurrencyCode AS SecondLastTradeCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC
) RowNumber -- ID DESC means most recent trade of ties
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
--need time filter???
) AS InnerSelect4SecondToLastTrade
WHERE InnerSelect4SecondToLastTrade.RowNumber = 2
) SecondToLastTrade ON SelectedContracts.MeasurableID = SecondToLastTrade.MeasurableID AND SelectedContracts.EntityID = SecondToLastTrade.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ContractPrice AS ContractPrice4ChangeCalc,
ID AS ContractID4ChangeCalc,
UTCMatched AS ContractUTC4ChangeCalc,
NumberOfContracts AS ContractsNumberTraded4ChangeCalc,
CurrencyCode AS ContractCurrency4ChangeCalc
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
ID DESC -- ID DESC equals the most recent trade if ties
) RowNumber
FROM
Contracts
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
AND dbo.Contracts.UTCmatched < DATEADD(Day ,-30, SYSDATETIME())
) AS InnerSelect4ChangeCalcPerPeriod
WHERE InnerSelect4ChangeCalcPerPeriod.RowNumber = 1
) Trade4ChangeCalcPerPeriod ON SelectedContracts.MeasurableID = Trade4ChangeCalcPerPeriod.MeasurableID AND SelectedContracts.EntityID = Trade4ChangeCalcPerPeriod.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ID AS HighestBidID,
MemberID AS HighestBidMemberID,
BidPrice AS HighestBidPrice,
AvailableContracts AS HighestBidAvailableContracts,
CurrencyCode AS HighestBidCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
BidPrice DESC,
ID DESC
) RowNumber
FROM
dbo.Interest2Buy
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND AvailableContracts > 0
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4HighestBid
WHERE InnerSelect4HighestBid.RowNumber = 1
) HighestBids ON SelectedContracts.MeasurableID = HighestBids.MeasurableID AND SelectedContracts.EntityID = HighestBids.EntityID
LEFT JOIN
(
SELECT
MeasurableID,
EntityID,
ID AS LowestAskID,
MemberID AS LowestAskMemberID,
AskPrice AS LowestAskPrice,
AvailableContracts AS LowestAskAvailableContracts,
CurrencyCode AS LowestAskCurrency
FROM
(
SELECT
*, ROW_NUMBER () OVER (
PARTITION BY MeasurableID,
EntityID
ORDER BY
AskPrice ASC,
ID DESC
) RowNumber
FROM
dbo.Interest2Sell
WHERE
MeasurableID IN ((2030),(2017),(2018),(2019),(2020),( 2028),(2024),(2027),(2029),(2022),( 4018),(4019),(4020),(4021))
AND AvailableContracts > 0
AND ( CurrencyCode IN (('GBP'), ('CAD'), ('INR'), ('BRL'), ('MXN'), ('CHF'), ('RUB'))
)
) AS InnerSelect4BestAsk
WHERE InnerSelect4BestAsk.RowNumber = 1
) BestAsks ON SelectedContracts.MeasurableID = BestAsks.MeasurableID AND SelectedContracts.EntityID = BestAsks.EntityID
正如您在问题中提到的，标量函数和多语句 table 值函数 (mTVF) 都是 "black boxes" 优化器...
所以，我的问题是 "why is this so bad?"。答案是，为了想出一个尽可能高效执行的好计划，它需要了解有关特定要求的某些细节以及有关它将从中提取数据的 tables 的信息（这就是为什么过时的静态也会严重影响性能的原因）。所以...当您使用标量函数或 mTVF 时，优化器无法像使用内联代码那样评估所有需求。它的反应是简单地假设该函数只会执行一次并根据该假设制定计划。
由于假设是错误的，因此生成了错误的计划，最终导致糟糕的表现。
解决方案是重写有问题的函数...关键是#1，确保将它们重写为 "inline table valued functions" (iTVF)。这些是优化器将看到的唯一函数，就好像它们的代码直接输入到外部查询中一样（因此术语 "inline"）。如果您不熟悉 iTVF，它们有 2 个要求……1 它们必须是 table 函数（无论出于何种原因，MS STILL 还没有可用的标量版本）……以及…… 2 这是大问题...函数体必须是单个语句。
那么，如果您不需要 table 值函数，您需要标量函数怎么办？好吧，没有什么说多值函数不能 return 单个（标量）值......这就是为什么那些知道这种情况的人将他们的所有函数都编码为 iTVF。
好在网络上不乏关于创建 "inline scalar functions" 的信息，使用编码为 return 标量值的 table 函数。
希望这对您有所帮助...
使用连接代替 "IN" 子句帮助很大。 （尽管我还将 table var 更改为临时变量 table，这也有很大帮助。）