C# 如何分组并包含零和

我试图编写一个查询，返回用户在我的应用程序中创建的每个类别中的事务总数。我的当前查询工作正常，但如果尚未在该类别下进行任何交易，则不会显示该类别。我希望我的查询显示每个类别，即使所有内容的总和为0

我查了一下怎么做，有人建议我使用左/右外连接，但它不能满足我的要求

我正在通过Windows C应用程序访问Microsoft Access 2007数据库。这是我当前的查询：

SELECT Categories.CategoryName ,
       SUM( Transactions.TransactionCredit ) as CreditSum ,
       SUM( Transactions.TransactionDebit  ) as DebitSum  ,
       SUM( Transactions.TransactionCredit ) -
       SUM( Transactions.TransactionDebit  ) as Difference ,
       SUM( Transactions.TransactionDebit  ) /
       ( SELECT SUM(TransactionDebit)
         FROM Transactions
         WHERE AccountID = {currentAccountId}
       ) as 'Percent of Total Debit'
FROM Categories
LEFT JOIN Transactions on Categories.CategoryName = Transactions.CategoryName
WHERE Transactions.AccountID = {currentAccountId}
  AND TransactionDate >= {startDate}
  AND TransactionDate <= {endDate}
GROUP BY Categories.CategoryName

这是我的c应用程序中的编码方式：

queries.returnQuery("SELECT Categories.CategoryName, " +
"SUM(Transactions.TransactionCredit) as CreditSum, " +
"SUM(Transactions.TransactionDebit) as DebitSum, " +
"SUM(Transactions.TransactionCredit) - SUM(Transactions.TransactionDebit) as Difference, " +
"SUM(Transactions.TransactionDebit) / (SELECT SUM(TransactionDebit) FROM Transactions WHERE AccountID = " + currentAccountID + ") as 'Percent of Total Debit' " +
"FROM Categories LEFT JOIN Transactions on Categories.CategoryName = Transactions.CategoryName " +
"WHERE Transactions.AccountID = " + currentAccountID +
(enableDateFilter ? " AND Transactions.TransactionDate >= #" + startDate + "# AND Transactions.TransactionDate <= #" + endDate + "# " : " ") +
" GROUP BY Categories.CategoryName");

---

如果没有双引号，您的查询将更容易理解。在任何情况下，问题在于where子句引用事务表，从而撤消左侧外部联接。将这些条件移到on子句中。在您的情况下，通过更改到何处和：

当您在类别和事务之间使用左连接时，您应该期望事务表上的值为NULL。在JOIN子句中包含AccountID筛选器将起到以下作用：

DECLARE @currentAccountId INT
SELECT  @currentAccountId = 1

;WITH   Transactions AS
(
    SELECT  *
    FROM    (   
    VALUES
                (1, 1000., 2000., 'Category B'),
                (2, 2000., 1000., 'Category B'),
                (1, 1000., 1000., 'Category C')
            )
            T ( AccountID, TransactionCredit, TransactionDebit, CategoryName)
),      Categories AS
(
    SELECT  *
    FROM    (
    VALUES
                ('Category A'),
                ('Category B'),
                ('Category C')
            )
            C (CategoryName)
)
SELECT      Categories.CategoryName ,
            SUM( Transactions.TransactionCredit ) as CreditSum ,
            SUM( Transactions.TransactionDebit  ) as DebitSum  ,
            SUM( Transactions.TransactionCredit ) -
            SUM( Transactions.TransactionDebit  ) as Difference ,
            SUM( Transactions.TransactionDebit  ) /
            (
                SELECT  SUM(TransactionDebit)
                FROM    Transactions
                WHERE   AccountID = @currentAccountId
            ) AS 'Percent of Total Debit'
FROM        Categories
LEFT JOIN   Transactions
    ON      Categories.CategoryName = Transactions.CategoryName
            AND Transactions.AccountID = @currentAccountId
            --AND TransactionDate >= {startDate}
            --AND TransactionDate <= {endDate}
GROUP BY    Categories.CategoryName

---

我面临的问题是，当使用联接时，必须使用将两个表比较在一起的条件。就我而言，我没有那样做。我使用了用户在c应用程序中选择的参数，因此我使用了一个子查询来代替事务表，并得到了预期的结果。请参见下面我的解决方案：

C中的解决方案：

queries.returnQuery("SELECT Categories.CategoryName, " +
                           "SUM(SUBQUERY.TransactionCredit) as CreditSum, " +
                           "SUM(SUBQUERY.TransactionDebit) as DebitSum, " +
                           "SUM(SUBQUERY.TransactionCredit) - SUM(SUBQUERY.TransactionDebit) as Difference " +
                           "FROM Categories LEFT JOIN " +
                               "(SELECT CategoryName, TransactionCredit, TransactionDebit FROM Transactions WHERE AccountID = " + currentAccountID + 
                               (enableDateFilter ? " AND TransactionDate >= #" + startDate + "# AND TransactionDate <= #" + endDate + "# " : " ") + 
                               ") AS SUBQUERY " + 
                           "ON Categories.CategoryName = SUBQUERY.CategoryName " +
                           "GROUP BY Categories.CategoryName");

解决方案不在C中：

SELECT Categories.CategoryName ,
       SUM( SUBQUERY.TransactionCredit ) as CreditSum ,
       SUM( SUBQUERY.TransactionDebit  ) as DebitSum  ,
       SUM( SUBQUERY.TransactionCredit ) -
       SUM( SUBQUERY.TransactionDebit  ) as Difference ,
       SUM( SUBQUERY.TransactionDebit  ) /
       ( SELECT SUM(TransactionDebit)
         FROM Transactions
         WHERE AccountID = {currentAccountId}
       ) as 'Percent of Total Debit'
FROM Categories
LEFT JOIN 
(
    SELECT CategoryName, 
           TransactionCredit, 
           TransactionDebit 
    FROM Transactions 
    WHERE AccountID = {currentAccountID}
      AND TransactionDate >= {startDate}
      AND TransactionDate <= {endDate}
) as SUBQUERY 
ON Categories.CategoryName = SUBQUERY.CategoryName
GROUP BY Categories.CategoryName

---

我为此道歉。我必须用C写，所以我只是复制粘贴它。但是，您所说的将导致错误JOIN表达式，而不是supported@Flappy . . . 原因是左外连接，MS Access称之为左连接。我将其更改为左连接，但仍然无法解决问题。虽然Nicholas重新格式化了我的问题，因此现在查询更容易阅读。而且，这也不是原因，因为如果我将WHERE留在其中，查询工作会非常好。如果我将它改为，并且得到错误的JOIN表达式not supportedOk，但是@Rubens，这个方法就不能像我在Gordon的帖子中所说的那样工作。当我为左连接包含多个条件时，我得到了不支持的错误连接表达式。如果我将第一个和更改为a，则查询可以正常工作，但不会产生预期的结果。

queries.returnQuery("SELECT Categories.CategoryName, " +
                           "SUM(SUBQUERY.TransactionCredit) as CreditSum, " +
                           "SUM(SUBQUERY.TransactionDebit) as DebitSum, " +
                           "SUM(SUBQUERY.TransactionCredit) - SUM(SUBQUERY.TransactionDebit) as Difference " +
                           "FROM Categories LEFT JOIN " +
                               "(SELECT CategoryName, TransactionCredit, TransactionDebit FROM Transactions WHERE AccountID = " + currentAccountID + 
                               (enableDateFilter ? " AND TransactionDate >= #" + startDate + "# AND TransactionDate <= #" + endDate + "# " : " ") + 
                               ") AS SUBQUERY " + 
                           "ON Categories.CategoryName = SUBQUERY.CategoryName " +
                           "GROUP BY Categories.CategoryName");

SELECT Categories.CategoryName ,
       SUM( SUBQUERY.TransactionCredit ) as CreditSum ,
       SUM( SUBQUERY.TransactionDebit  ) as DebitSum  ,
       SUM( SUBQUERY.TransactionCredit ) -
       SUM( SUBQUERY.TransactionDebit  ) as Difference ,
       SUM( SUBQUERY.TransactionDebit  ) /
       ( SELECT SUM(TransactionDebit)
         FROM Transactions
         WHERE AccountID = {currentAccountId}
       ) as 'Percent of Total Debit'
FROM Categories
LEFT JOIN 
(
    SELECT CategoryName, 
           TransactionCredit, 
           TransactionDebit 
    FROM Transactions 
    WHERE AccountID = {currentAccountID}
      AND TransactionDate >= {startDate}
      AND TransactionDate <= {endDate}
) as SUBQUERY 
ON Categories.CategoryName = SUBQUERY.CategoryName
GROUP BY Categories.CategoryName