在带有查询优化器热修复的 SQL Server 2017（RTM-CU17）上，我有一个索引视图需要花费大量时间来更新。我不知所措，无法弄清楚为什么要进行全表扫描以进行更新。
索引视图有一个总和，并将主键上的两个表连接到具有高选择性的外键（每个主键平均 5 个外行）。如果更新了主表行，则通常会在外键表中查找聚合数据。如果该行有一个超出直方图范围的键（高于 RANGE_HI_KEY 的最大值），它决定使用外键对辅助表进行表扫描，即使辅助表在统计信息中有键值也是如此。我在生产中得到的估计有 1.1 亿行，但实际只有 6 行……相距甚远。由于它是升序键中的热数据，因此它实际上在找到所需的 6 行之前读取了所有 1.1 亿行。
我发现一个已修补的 Microsoft 问题与正在发生的事情非常相似，但在这种情况下没有纠正它：https: //support.microsoft.com/en-us/help/3192154/a-non-optimal-query -plan-choice-causes-poor-performance-when-values
由于我无法共享生产代码，我可以简单地重新创建它，并且可以在此处找到计划，一个带有边界搜索，一个带有越界扫描： https ://www.brentozar.com/pastetheplan/?id =SknQqFzy8
这是我用来创建上述计划的 SQL……非常简单。我不确定为什么会发生扫描，非常感谢任何帮助！
--SQL Server 2017 (TRM-CU17), compatability 140, Query Optimizer Hotfixes on
CREATE TABLE dbo.tblTrans
(id INT IDENTITY(1,1) NOT NULL,
CustID INT NOT NULL,
Flag SMALLINT NOT NULL)
GO
ALTER TABLE [dbo].[tblTrans] ADD CONSTRAINT [PK_tblTrans_ID] PRIMARY KEY CLUSTERED ([ID]) WITH (FILLFACTOR=90) ON [PRIMARY]
GO
--insert random sample of data
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),9)
GO 10
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),3)
GO 225
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),7)
GO 25
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),4)
GO 185
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),5)
GO 150
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),8)
GO 15
INSERT INTO dbo.tblTrans (CustID, Flag)
VALUES (FLOOR(RAND()*1000),2)
GO 110
CREATE TABLE dbo.tblTrans_Detail
(id INT IDENTITY(1,1) NOT NULL,
transid INT NOT NULL,
Amount MONEY NOT NULL)
GO
ALTER TABLE [dbo].[tblTrans_Detail] ADD CONSTRAINT [PK_tblTrans_Detail_ID] PRIMARY KEY CLUSTERED ([ID]) WITH (FILLFACTOR=90) ON [PRIMARY]
GO
--insert random data into detail table
INSERT INTO dbo.tblTrans_Detail (transid, Amount)
SELECT id, CustID+10 AS amount
FROM dbo.tblTrans
INSERT INTO dbo.tblTrans_Detail (transid, Amount)
SELECT id, CustID+12 AS amount
FROM dbo.tblTrans
INSERT INTO dbo.tblTrans_Detail (transid, Amount)
SELECT id, CustID+13 AS amount
FROM dbo.tblTrans
GO
CREATE VIEW [dbo].[ivw_Get_Trans]
WITH SCHEMABINDING
AS
SELECT
dbo.tblTrans.CustID ,
SUM(dbo.tblTrans_Detail.Amount) AS Amount,
COUNT_BIG(*) AS CBCount
FROM dbo.tblTrans
INNER JOIN dbo.tblTrans_Detail
ON tblTrans.id = tblTrans_Detail.TransID
WHERE ( dbo.tblTrans.Flag = 2 )
GROUP BY dbo.tblTrans.CustID
GO
CREATE UNIQUE CLUSTERED INDEX [idx_vw_Trans] ON [dbo].[ivw_Get_Trans] (
[CustID]
) WITH (FILLFACTOR=90, STATISTICS_NORECOMPUTE=OFF) ON [PRIMARY]
GO
--DBCC SHOW_STATISTICS ('dbo.tbltrans',pk_tbltrans_id)
--MAX RANGE_HI_KEY is 720 (also max id from table), key is selective
INSERT INTO dbo.tbltrans (CustID, Flag)
OUTPUT Inserted.id
VALUES (100, 5)
GO
--ID 721 is inserted
INSERT INTO dbo.tbltrans_detail (transid, Amount)
VALUES (721,13.00)
GO
--new ID is in stats of detail table but not stats for trans table
CREATE INDEX IX_tblTrans_Detail_TransID ON dbo.tbltrans_detail (TransID, Amount)
GO
--DBCC SHOW_STATISTICS ('dbo.tbltrans_detail',ix_tbltrans_detail_Transid)
--DBCC FREEPROCCACHE
--set showplan on
BEGIN TRANSACTION
UPDATE dbo.tblTrans
SET Flag = 2
WHERE ID = 720 --seek (highest value in histogram, tblTrans)
--WHERE ID = 721 --scan (out of bounds in histogram, tblTrans)
UPDATE dbo.tblTrans
SET Flag = 2
--WHERE ID = 720 --seek (highest value in histogram, tblTrans)
WHERE ID = 721 --scan (out of bounds in histogram, tblTrans)
ROLLBACK TRANSACTION
--DROP view dbo.ivw_Get_Trans
--drop table dbo.tblTrans
--drop table dbo.tblTrans_Detail