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用SQL Server查询累计值

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Jun 07, 2016 pm 04:18 PM

serverInquire

有这样一个要求，它要创建一个SQL Server查询，其中包括基于事件时刻的累计值。典型的例子就是一个银行账户，因为你每一次都是在不同的时间去存钱和取钱。对任意一个账户来说，在某个时间点都要算出它的借(存款)和贷(取款)之和。每一笔交易之后，你都想知道

　　有这样一个要求，它要创建一个SQL Server查询，其中包括基于事件时刻的累计值。典型的例子就是一个银行账户，因为你每一次都是在不同的时间去存钱和取钱。对任意一个账户来说，在某个时间点都要算出它的借(存款)和贷(取款)之和。每一笔交易之后，你都想知道当前的余额。列表A创建了这样一个表格的简单的例子。

　　列表A

用SQL Server查询累计值

　　下面是一些示例行：

　　1 2006-11-03 02:33:42.34010000.00

　　2 2006-11-03 02:34:50.467-500.00

　　3 2006-11-03 02:35:04.857250.00

　　4 2006-11-03 02:42:19.763-124.25

　　因为日期是缺省设定的，你要做的就是加入一些金额。例子中为了简单起见，假设只有一个银行账户(为了更符合实际情况，可以添加一个BankAccountNumber列)。

　　现在你就能够创建一个包括了当前余额的查询。因为你已经在同一列中用正负数值记录了存款和取款值，所以列中的累计值是很容易算出的。你要得到当前的余额，就要计算出以前所有交易的总值，然后将这个值和当前的交易相加。列表B中的查询实现了这一点。

　　列表B

用SQL Server查询累计值

　　这样就得到了以下的结果集：

　　1 2006-11-03 02:33:42.34010000.00 10000.00

　　2 2006-11-03 02:34:50.467-500.00 9500.00

　　3 2006-11-03 02:35:04.857250.00 9750.00

　　4 2006-11-03 02:42:19.763-124.25 9625.75

　　如这个例子所示，只要你理解了要求，就可以很容易地建立累计值。所示的例子假设表格中只包括一个账户，但是要处理多个账户也很简单。添加一个BankAccountNumber 列和一个指定利息数量的WHERE谓词即可。

　　你也可以把这个例子倒过来用，如在一个存货计算中创建一个不同的运行。你从存货1，000开始，然后减去各种花销和收据。

　　这样的查询有两个优点：

　　你不需要储存结果。当用账户编号或外键操作时，执行可以如闪电般迅速。

　　你以一个标签结束事务，它可以逐行进行检查。如果出现问题的话，你可以将导致问题出现的事务隔离。

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