如何使用两个派生表创建公用表表达式

Question

所以我尝试用两个派生表创建这个 CTE。我的第一个派生表将显示 500 范围内的帐号、帐号描述。 CTE 中的第二个派生表 - 应列出发票总数大于 1000 的帐号、发票总数和发票 ID。

现在我开始分别创建这两个表，以确保我知道自己在做什么。他们是这样工作的：

SELECT AccountNo, 
    AccountDescription
FROM Accounts
WHERE AccountNo BETWEEN 500 and 599

SELECT Accounts.AccountNo, 
    Invoices.InvoiceTotal, 
    Invoices.InvoiceID
FROM Accounts 
    JOIN InvoiceLineItems
        ON Accounts.AccountNo = InvoiceLineItems.AccountNo
    JOIN Invoices
        ON InvoiceLineItems.InvoiceID = Invoices.InvoiceID
WHERE Invoices.InvoiceTotal >= 1000

现在，当我尝试将它们变成 CTE 时，我的最佳尝试如下所示：

WITH Accounts500to599 AS
(SELECT AccountNo, 
    AccountDescription
FROM Accounts
WHERE AccountNo BETWEEN 500 and 599
ORDER BY Accounts.AccountNo),

InvoicesAbove1000 AS 
(SELECT Accounts.AccountNo, 
    Invoices.InvoiceTotal, 
    Invoices.InvoiceID
FROM Accounts 
    JOIN InvoiceLineItems
        ON Accounts.AccountNo = InvoiceLineItems.AccountNo
    JOIN Invoices
        ON InvoiceLineItems.InvoiceID = Invoices.InvoiceID
WHERE Invoices.InvoiceTotal >= 1000
ORDER BY Accounts.AccountNo)

现在我的最终目标是显示发票大于平均发票总额的帐户，这应该很简单，但在创建这些 CTE 时我还有很多东西要学。

任何建议将不胜感激。谢谢。

Answer 1

像对待任何其他表（或视图）一样对待 CTE。它会创建一个虚拟表以供使用。

例如，在你上面，你可以这样做

WITH Accounts500to599 AS
(SELECT AccountNo, 
    AccountDescription
FROM Accounts
WHERE AccountNo BETWEEN 500 and 599
-- ORDER BY Accounts.AccountNo -- Note - removed the order by
),

InvoicesAbove1000 AS 
(SELECT Accounts.AccountNo, 
    Invoices.InvoiceTotal, 
    Invoices.InvoiceID
FROM Accounts 
    JOIN InvoiceLineItems
        ON Accounts.AccountNo = InvoiceLineItems.AccountNo
    JOIN Invoices
        ON InvoiceLineItems.InvoiceID = Invoices.InvoiceID
WHERE Invoices.InvoiceTotal >= 1000
--ORDER BY Accounts.AccountNo   -- Note - removed the order by
)

SELECT A.AccountNo, A.AccountDescription, AVG(I.InvoiceTotal) AS AvgInvoiceTotal
FROM   Accounts500to599 A
       INNER JOIN InvoicesAbove1000 I ON A.AccountNo = I.AccountNo
GROUP BY A.AccountNo, A.AccountDescription

这并不能回答您的“发票高于平均水平”，因为当您已经排除了小于 1000 美元的发票时，这实际上意味着什么存在一些问题，但上面给出了如何使用它们的示例。

请注意，数据的顺序无关紧要（就像普通表一样） - 因此我在 CTE 中注释掉了 ORDER BY 子句。

传统的 CTE 在功能上也等同于 FROM 子句中的子查询 - 所以上面类似于

SELECT A.AccountNo, A.AccountDescription, AVG(I.InvoiceTotal) AS AvgInvoiceTotal
FROM   (SELECT AccountNo, 
               AccountDescription
        FROM Accounts
        WHERE AccountNo BETWEEN 500 and 599
       ) A
       INNER JOIN 
      (SELECT Accounts.AccountNo, 
          Invoices.InvoiceTotal, 
         Invoices.InvoiceID
       FROM Accounts 
           JOIN InvoiceLineItems
                ON Accounts.AccountNo = InvoiceLineItems.AccountNo
           JOIN Invoices
                ON InvoiceLineItems.InvoiceID = Invoices.InvoiceID
      WHERE Invoices.InvoiceTotal >= 1000
    ) I ON A.AccountNo = I.AccountNo
GROUP BY A.AccountNo, A.AccountDescription

Answer 2

作为对 seanb 答案的扩展，您可以通过以下方式尝试使您的发票高于平均发票金额。看看WHERE。

;WITH Accounts500to599 AS (
    SELECT
        AccountNo, 
        AccountDescription
    FROM AS Accounts
    WHERE
        AccountNo BETWEEN 500 and 599
),
InvoicesAbove1000 AS (
    SELECT
        Accounts.AccountNo, 
        Invoices.InvoiceTotal, 
        Invoices.InvoiceID
    FROM Accounts 
        JOIN InvoiceLineItems
            ON Accounts.AccountNo = InvoiceLineItems.AccountNo
        JOIN Invoices
            ON InvoiceLineItems.InvoiceID = Invoices.InvoiceID
    WHERE 
        Invoices.InvoiceTotal >= 1000
)
SELECT
    Accounts500to599.AccountNo,
    Accounts500to599.AccountDescription,
    InvoicesAbove1000.InvoiceID,
    InvoicesAbove1000.InvoiceTotal
FROM Accounts500to599
INNER JOIN InvoicesAbove1000
    ON Accounts500to599.AccountNo = InvoicesAbove1000.AccountNo
WHERE InvoicesAbove1000.InvoiceTotal > (
    
    SELECT 
        AVG( InvoiceTotal )
    FROM Accounts AS a
    INNER JOIN InvoiceLineItems l
        ON a.AccountNo = l.AccountNo
    INNER JOIN Invoices i
        ON l.InvoiceID = i.InvoiceID
    WHERE
        a.AccountNo BETWEEN 500 AND 599
        AND i.InvoiceTotal > 1000

)
ORDER BY
    Accounts500to599.AccountNo;