重用SQL中的子查询列

我有下面的SQL

SELECT  U.ID AS UserID
    ,U.LoginName AS Name
    ,PV.Time AS [Time]
    ,PV.URL AS [Url]
    ,P.Name AS [Product 1 Name]
    ,P.SKU AS [Product 1 SKU]
    ,P.ModelNumber AS [Product 1 Model Number]
    ,P2.Name AS [Product 2 Name]
    ,P2.SKU AS [Product 2 SKU]
    ,P2.ModelNumber AS [Product 2 Model Number]
    ,ISNULL((select TOP 1 Value from AttributesValues AV INNER JOIN Attributes A ON AV.AttributeID = A.ID WHERE AV.ProductID = P.ID AND A.RetailerID = 23 AND A.CODE = 'metadata-department'),'') AS Department
        ,ISNULL((select TOP 1 Value from AttributesValues AV INNER JOIN Attributes A ON AV.AttributeID = A.ID WHERE AV.ProductID = P.ID AND A.RetailerID = 23 AND A.CODE = 'metadata-group'),'') AS Department
        ,ISNULL((select TOP 1 Value from AttributesValues AV INNER JOIN Attributes A ON AV.AttributeID = A.ID WHERE AV.ProductID = P.ID AND A.RetailerID = 23 AND A.CODE = 'metadata-subgroup'),'') AS SubGroup
        ,C.Browser AS [Browser]
        ,C.BrowserVersion AS [Browser Version]
        ,C.IPAddress AS [IP Address]
        ,C.UserAgent AS [User Agent]
        ,C.UserLanguage AS [User Language]
        ,PV.PageType AS [Page Type]
FROM    PageVisits PV
        INNER JOIN Users U ON U.ID = PV.UserID
        INNER JOIN Clients C ON C.ID = PV.ClientID
        INNER JOIN Products P ON P.id = PV.P1ID 
        LEFT OUTER JOIN Products P2 ON P2.id = PV.P2ID 
WHERE   P.RetailerID = 23 
        AND PV.UserID IS NOT NULL
        AND PV.PageType IN ('Product','Compare Products')
        AND PV.[Time] >= '{0}' AND PV.[Time] < '{1}'

---

我在这里用了三次。唯一的区别是A.CODE=。如何改进这一点

您应该首先尝试为查询建立索引：

create index on Attributes(RetailerId, Code, Id);
create index on AttributeValues(AttributeId, ProductId, Value);

---

子查询的处理应该只是几个索引查找。

您应该首先尝试为查询构建索引：

create index on Attributes(RetailerId, Code, Id);
create index on AttributeValues(AttributeId, ProductId, Value);

子查询的处理应该只是几个索引查找。

始终使用ORDER BY with TOP。否则，您将得到不确定的结果，这取决于SQL引擎将如何获取相关行

如果实际上不需要TOP 1，即如果子查询始终返回1或0行，而没有TOP，则可以使用EXTER APPLY with MAX：

始终使用带有顶部的ORDER BY。否则，您将得到不确定的结果，这取决于SQL引擎将如何获取相关行

如果实际上不需要TOP 1，即如果子查询始终返回1或0行，而没有TOP，则可以使用EXTER APPLY with MAX：

---

您可以定义一个CTE，它基本上是一个内联视图，以避免重新键入查询，但它实际上不会更改正在执行的查询3次，它只会整理代码：

WITH CTE AS
(   SELECT  AV.ProductID, AV.Value, A.Code 
    FROM    AttributesValues AV 
            INNER JOIN Attributes A ON AV.AttributeID = A.ID 
    WHERE   A.RetailerID = 23
)
SELECT  U.ID AS UserID
        ,U.LoginName AS Name
        ,PV.Time AS [Time]
        ,PV.URL AS [Url]
        ,P.Name AS [Product 1 Name]
        ,P.SKU AS [Product 1 SKU]
        ,P.ModelNumber AS [Product 1 Model Number]
        ,P2.Name AS [Product 2 Name]
        ,P2.SKU AS [Product 2 SKU]
        ,P2.ModelNumber AS [Product 2 Model Number]
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-department'),'') AS Department
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-group'),'') AS [Group]
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-subgroup'),'') AS SubGroup
        ,C.Browser AS [Browser]
        ,C.BrowserVersion AS [Browser Version]
        ,C.IPAddress AS [IP Address]
        ,C.UserAgent AS [User Agent]
        ,C.UserLanguage AS [User Language]
        ,PV.PageType AS [Page Type]
FROM    PageVisits PV
        INNER JOIN Users U ON U.ID = PV.UserID
        INNER JOIN Clients C ON C.ID = PV.ClientID
        INNER JOIN Products P ON P.id = PV.P1ID 
        LEFT OUTER JOIN Products P2 ON P2.id = PV.P2ID 
WHERE   P.RetailerID = 23 
        AND PV.UserID IS NOT NULL
        AND PV.PageType IN ('Product','Compare Products')
        AND PV.[Time] >= '{0}' AND PV.[Time] < '{1}'

---

N> B您可能希望更改行号中的ORDER BY，以影响productID和代码的每个组合返回的值。如果这是唯一的，ORDER BY是不相关的，尽管*

您可以定义一个CTE，它基本上是一个内联视图，以避免重新键入查询，但实际上不会更改正在执行的查询3次，它只会整理代码：

WITH CTE AS
(   SELECT  AV.ProductID, AV.Value, A.Code 
    FROM    AttributesValues AV 
            INNER JOIN Attributes A ON AV.AttributeID = A.ID 
    WHERE   A.RetailerID = 23
)
SELECT  U.ID AS UserID
        ,U.LoginName AS Name
        ,PV.Time AS [Time]
        ,PV.URL AS [Url]
        ,P.Name AS [Product 1 Name]
        ,P.SKU AS [Product 1 SKU]
        ,P.ModelNumber AS [Product 1 Model Number]
        ,P2.Name AS [Product 2 Name]
        ,P2.SKU AS [Product 2 SKU]
        ,P2.ModelNumber AS [Product 2 Model Number]
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-department'),'') AS Department
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-group'),'') AS [Group]
        ,ISNULL((SELECT TOP 1 Value FROM CTE WHERE CTE.ProductID = P.ID AND CTE.CODE = 'metadata-subgroup'),'') AS SubGroup
        ,C.Browser AS [Browser]
        ,C.BrowserVersion AS [Browser Version]
        ,C.IPAddress AS [IP Address]
        ,C.UserAgent AS [User Agent]
        ,C.UserLanguage AS [User Language]
        ,PV.PageType AS [Page Type]
FROM    PageVisits PV
        INNER JOIN Users U ON U.ID = PV.UserID
        INNER JOIN Clients C ON C.ID = PV.ClientID
        INNER JOIN Products P ON P.id = PV.P1ID 
        LEFT OUTER JOIN Products P2 ON P2.id = PV.P2ID 
WHERE   P.RetailerID = 23 
        AND PV.UserID IS NOT NULL
        AND PV.PageType IN ('Product','Compare Products')
        AND PV.[Time] >= '{0}' AND PV.[Time] < '{1}'

---

N> B您可能希望更改行号中的ORDER BY，以影响productID和代码的每个组合返回的值。如果这是唯一的，则ORDER BY与问题无关*

与问题无关：TOP应仅与ORDER BY一起使用。创建视图以缩短子查询中的子查询，你有一个没有订单的TOP BY。准备临时表subquery@ypercube，这有什么区别吗？与问题无关：TOP应仅与ORDER BY一起使用。创建视图以缩短子查询在子查询中，您有TOP而没有ORDER BY。准备临时表subquery@ypercube，这有什么区别吗？好的。但是有人告诉我索引会使INSERT/UPDATE/DELETE变慢？@user960567这取决于对这些语句感兴趣的列以及索引定义中设置的列。@user960567。索引将降低数据插入操作的速度。是否使用它们取决于系统上的相对负载。这个问题没有涉及数据修改负载。+1，索引建议非常有用@在user960567中，索引通常会增强使用它们的SELECT查询和一些INSERT/UPDATE/DELETE查询，并带来巨大的性能优势。插入和某些更新/删除的速度通常很慢。确定。但是有人告诉我索引会使INSERT/UPDATE/DELETE变慢？@user960567这取决于对这些语句感兴趣的列以及索引定义中设置的列。@user960567。索引将降低数据插入操作的速度。是否使用它们取决于系统上的相对负载。这个问题没有涉及数据修改负载。+1，索引建议非常有用@在user960567中，索引通常会增强使用它们的SELECT查询和一些INSERT/UPDATE/DELETE查询，并带来巨大的性能优势。插入和某些更新/删除的速度通常很慢。

WITH CTE AS
(   SELECT  AV.ProductID, 
            AV.Value, 
            A.Code ,
            RowNumber = ROW_NUMBER() OVER(PARTITION BY AV.ProductID, A.Code ORDER BY AV.Value)
    FROM    AttributesValues AV 
            INNER JOIN Attributes A ON AV.AttributeID = A.ID 
    WHERE   A.RetailerID = 23
    AND     AV.Code IN ('metadata-department', 'metadata-group', 'metadata-subgroup')
), AV AS
(   SELECT  pvt.ProductID, 
            pvt.[metadata-department], 
            pvt.[metadata-group], 
            pvt.[metadata-subgroup]
    FROM    CTE
            PIVOT
            (   MAX(Value)
                FOR Code IN ([metadata-department], [metadata-group], [metadata-subgroup])
            ) pvt
    WHERE   pvt.RowNumber = 1
)
SELECT  U.ID AS UserID
        ,U.LoginName AS Name
        ,PV.Time AS [Time]
        ,PV.URL AS [Url]
        ,P.Name AS [Product 1 Name]
        ,P.SKU AS [Product 1 SKU]
        ,P.ModelNumber AS [Product 1 Model Number]
        ,P2.Name AS [Product 2 Name]
        ,P2.SKU AS [Product 2 SKU]
        ,P2.ModelNumber AS [Product 2 Model Number]
        ,ISNULL(AV.[metadata-department],'') AS Department
        ,ISNULL(AV.[metadata-group],'') AS [Group]
        ,ISNULL(AV.[metadata-subgroup],'') AS SubGroup
        ,C.Browser AS [Browser]
        ,C.BrowserVersion AS [Browser Version]
        ,C.IPAddress AS [IP Address]
        ,C.UserAgent AS [User Agent]
        ,C.UserLanguage AS [User Language]
        ,PV.PageType AS [Page Type]
FROM    PageVisits PV
        INNER JOIN Users U ON U.ID = PV.UserID
        INNER JOIN Clients C ON C.ID = PV.ClientID
        INNER JOIN Products P ON P.id = PV.P1ID 
        LEFT OUTER JOIN Products P2 ON P2.id = PV.P2ID 
        LEFT OUTER JOIN AV ON AV.ProductID = p.ID
WHERE   P.RetailerID = 23 
        AND PV.UserID IS NOT NULL
        AND PV.PageType IN ('Product','Compare Products')
        AND PV.[Time] >= '{0}' AND PV.[Time] < '{1}'