如何消除分区视图中的表

Question

我无法获得将常规表连接到分区视图以消除不符合分区列谓词的表的查询。特别是，我对我对分区视图进行 LEFT OUTER JOIN 并且我的谓词涵盖一系列值的情况感兴趣。当我修改查询以使用 INNER JOIN 或将谓词限制为单个值时，表被正确消除。这是一个演示该问题的脚本。我在 SQL Server 2016 SP1 中对此进行了测试。

--Create 2 tables for prices; 1 for 2017 and 1 for 2018
CREATE TABLE Price_2017
(
    PriceDate DATE NOT NULL,
    PriceValue FLOAT NOT NULL
)
GO

ALTER TABLE Price_2017 ADD CONSTRAINT PK_Price_2017 PRIMARY KEY(PriceDate);
GO

ALTER TABLE Price_2017 WITH CHECK ADD CONSTRAINT CK_Price_2017
CHECK (PriceDate >= '2017-01-01' AND PriceDate <= '2017-12-31');
GO

ALTER TABLE Price_2017 CHECK CONSTRAINT CK_Price_2017;
GO

CREATE TABLE Price_2018
(
    PriceDate DATE NOT NULL,
    PriceValue FLOAT NOT NULL
)
GO

ALTER TABLE Price_2018 ADD CONSTRAINT PK_Price_2018 PRIMARY KEY(PriceDate);
GO

ALTER TABLE Price_2018 WITH CHECK ADD CONSTRAINT CK_Price_2018
CHECK (PriceDate >= '2018-01-01' AND PriceDate <= '2018-12-31');
GO

ALTER TABLE Price_2018 CHECK CONSTRAINT CK_Price_2018;
GO

--Create a partitioned view for all dates
CREATE VIEW Price_All AS
SELECT p.PriceDate, p.PriceValue
 FROM dbo.Price_2017 p
UNION ALL 
SELECT p.PriceDate, p.PriceValue
 FROM dbo.Price_2018 p;

--Create some prices
INSERT INTO Price_2017 (PriceDate, PriceValue) VALUES('2017-01-01',1);
INSERT INTO Price_2017 (PriceDate, PriceValue) VALUES('2017-01-02',2);

INSERT INTO Price_2018 (PriceDate, PriceValue) VALUES('2018-01-01',10);
INSERT INTO Price_2018 (PriceDate, PriceValue) VALUES('2018-01-02',20);

--Create another table that we will relate to prices
CREATE TABLE Purchase
(
    PurchaseDate DATE NOT NULL,
    Quantity INT NOT NULL
)
GO

ALTER TABLE Purchase ADD CONSTRAINT PK_Purchase PRIMARY KEY(PurchaseDate);
GO

--Put some stuff in the other table
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2017-01-01', 1);
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2017-01-02', 2);
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2017-01-03', 3);
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2018-01-01', 4);
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2018-01-02', 5);
INSERT INTO Purchase (PurchaseDate, Quantity) VALUES ('2018-01-03', 6);

--Test Queries

--These are all good; the execution plan includes only necessary tables
SELECT * FROM Price_All WHERE PriceDate = '2017-01-01';
SELECT * FROM Price_All WHERE PriceDate = '2018-01-01';
SELECT * FROM Price_All WHERE PriceDate BETWEEN '2017-01-01' AND '2017-01-02';
SELECT * FROM Price_All WHERE PriceDate BETWEEN '2018-01-01' AND '2018-01-02';

--Good; doesn't seek in the 2018 table
--https://www.brentozar.com/pastetheplan/?id=BJ8RBqlYG
SELECT pu.PurchaseDate, pu.Quantity, pr.PriceValue
FROM Purchase pu
LEFT JOIN Price_All pr
ON pr.PriceDate = pu.PurchaseDate
WHERE pu.PurchaseDate = '2017-01-01';

--Good; doesn't seek in the 2018 table
--https://www.brentozar.com/pastetheplan/?id=SkOEUqgKG
SELECT pu.PurchaseDate, pu.Quantity, pr.PriceValue
FROM Purchase pu
INNER JOIN Price_All pr --notice, inner join
ON pr.PriceDate = pu.PurchaseDate
WHERE pu.PurchaseDate BETWEEN '2017-01-01' AND '2017-01-02'; --notice, range of dates

--Bad; seeks in both price tables
--https://www.brentozar.com/pastetheplan/?id=BkU8UcxFM
SELECT pu.PurchaseDate, pu.Quantity, pr.PriceValue
FROM Purchase pu
LEFT OUTER JOIN Price_All pr --notice, left join
ON pr.PriceDate = pu.PurchaseDate
WHERE pu.PurchaseDate BETWEEN '2017-01-01' AND '2017-01-02'; --notice, range of dates

我包含了指向最后三个查询的执行计划的链接。只有最后一个查询有问题（它在 2017 和 2018 表中执行查找，而它应该只在 2017 中查找）。在我的生产数据库中，这会导致性能非常差，并且阻碍了我推出特定日期表的能力，以处理当前存储在单个表中的 10 多亿行的维护开销。如何让 SQLServer 在上次查询中只使用 2017 表？

Answer 1

SQL Server 确实在消除 2018 分区，即使它出现在计划中。

计划中的启动表达式过滤器在执行时消除了不需要的 2018 表。在打开实际执行计划的情况下运行查询后，将鼠标悬停在 Price_2018 表的搜索上：

请注意，“执行次数”为 0。这意味着 SQL Server 在运行时消除了查找。

您还可以运行查询STATISTICS IO ON以查看仅触及 2017 表：

SET STATISTICS IO ON;
GO
SELECT pu.PurchaseDate, pu.Quantity, pr.PriceValue
FROM Purchase pu
LEFT OUTER JOIN Price_All pr --notice, left join
ON pr.PriceDate = pu.PurchaseDate
WHERE pu.PurchaseDate BETWEEN '2017-01-01' AND '2017-01-02'; --notice, range of dates

统计 IO 输出显示：

(2 rows affected)
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Price_2017'. Scan count 0, logical reads 4, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
Table 'Purchase'. Scan count 1, logical reads 2, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

Price_2018 表不在该列表中 - 这意味着它没有被触及。