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首先，对问题的一般描述：我正在运行一个定期进程，它会更新表格中的总数。问题是，流程的每次执行都可能需要多次更新，并且每次执行都取决于之前的结果。

我的问题是，可以在单个 SQL Server SP 中完成吗？

我的代码（我对其进行了一些更改以简化示例）：

INSERT INTO CustomerMinuteSessions(time, customer, sessions, bytes, previousTotalSessions)
SELECT MS.time,
           MS.customer,
           MS.totalSessions,
           MS.totalBytes,
           CTS.previousTotalSessions
FROM (SELECT time, customer, SUM(sessions) as totalSessions, SUM(bytes) AS totalBytes
      FROM MinuteSessions
      WHERE time > @time
      GROUP BY time, x) MS
CROSS APPLY TVF_GetPreviousCustomerTotalSessions(MS.customer) CTS
ORDER BY time

该previousTotalSessions列依赖于 中的其他行UpdatedTable，其值由CROSS APPLYing检索TVF_GetPreviousCustomerTotalSessions，但如果我按原样执行 SP，则所有行都使用函数检索到的值，而不采用SP 执行期间添加的行。

为了完整起见，这里是TVF_GetPreviousCustomerTotalSessions：

FUNCTION [dbo].[TVF_GetCustomerCurrentSessions] 
(   
    @customerId int
)
RETURNS @result TABLE (PreviousNumberOfSessions int)
AS
BEGIN
    INSERT INTO @result
    SELECT TOP 1 (PreviousNumberOfSessions + Opened - Closed) AS PreviousNumberOfSessions
    FROM CustomerMinuteSessions 
    WHERE CustomerId = @customerId 
    ORDER BY time DESC

    IF @@rowcount = 0
        INSERT INTO @result(PreviousNumberOfSessions) VALUES(0)

    RETURN
END

什么是最好的（即没有for循环，我猜......）在查询中获取后续行的前一行？

4

1 回答 1

0

如果您使用的是 SQL-2005 及更高版本，则可以一次性使用少量 CTE。如果您使用 SQL-2000，您将可以使用内联表值函数。

就我个人而言，我更喜欢 CTE 方法，因此我将您的代码转换为 CTE 语法的示意图。（请记住，我没有准备测试集来检查它）。

WITH LastSessionByCustomer AS  
(
    SELECT CustomerID, MAX(Time)
    FROM CustomerMinuteSessions
    GROUP BY CustomerID
)
, GetPreviousCustomerTotalSessions AS
(
    SELECT LastSession.CustomerID, LastSession.PreviousNumberOfSessions + LastSession.Opened - LastSession.Closed AS PreviousNumberOfSessions
    FROM CustomerMinuteSessions LastSession
    INNER JOIN LastSessionByCustomer ON LastSessionByCustomer.CustomerID = LastSession.CustomerID
)
, MS AS
(
    SELECT time, customer, SUM(sessions) as totalSessions, SUM(bytes) AS totalBytes
    FROM MinuteSessions
    WHERE time > @time
    GROUP BY time, x
)
INSERT INTO CustomerMinuteSessions(time, customer, sessions, bytes, previousTotalSessions)
SELECT MS.time,
           MS.customer,
           MS.totalSessions,
           MS.totalBytes,
           ISNULL(GetPreviousCustomerTotalSessions.previousTotalSessions, 0)
FROM MS 
RIGHT JOIN GetPreviousCustomerTotalSessions ON MS.Customer = GetPreviousCustomerTotalSessions.CustomerID

稍微超出您的问题，我认为一旦表 CustomerMinuteSessions 数据库增长，您的交叉应用查询可能会对数据库造成重大损害我会添加一个索引，例如以提高您获得 Index-Seek 的机会：

CREATE INDEX IX_CustomerMinuteSessions_CustomerId
    ON CustomerMinuteSessions (CustomerId, [time] DESC, PreviousNumberOfSessions, Opened, Closed );
于 2013-07-03T13:13:14.923 回答