突出显示缺少的后续付款 SQL Server答案

【问题标题】：Highlight missing follow up payment SQL Server突出显示缺少的后续付款 SQL Server
【发布时间】：2021-11-25 15:12:51
【问题描述】：

我正在尝试找到一种方法来创建一个查询，以突出显示预期交易是否遵循 SQL Server 2016 中的付款。

我掌握的数据大概是

SELECT 123456 AS Casekey
        , 1 as rnk
        , NULL AS LAPayment
        , 1080.00 AS LAReserve
UNION ALL
SELECT 123456 AS Casekey
        , 2 as rnk
        , 1080.00 AS LAPayment
        , null AS LAReserve
UNION ALL
SELECT 123456 AS Casekey
        , 3 as rnk
        , NULL AS LAPayment
        , NULL AS LAReserve

在 LAPayment 之后应该有一个 0 的后续 LAReserve，但是没有 - 我需要在发生这种情况时强调 - 基本上付款将储备金减少到 0，但系统配置的方式将 0 输入到交易屏幕和数据必须反映系统 - 遗憾的是，这超出了我的控制范围！

【问题讨论】：

你能添加预期的输出来解决问题吗？

标签： sql tsql sql-server-2016

【解决方案1】：

您可以为此使用LEAD 窗口函数

SELECT *
FROM (
    SELECT *,
      NextLAReserve = LEAD(LAReserve) OVER (PARTITION BY Casekey ORDER BY rnk)
    FROM YourTable t
) t
WHERE t.LAPayment > 0 AND t.NextLAReserve IS NULL;

【讨论】：

【解决方案2】：

Windows 函数在这方面很有用。在此问题中，您可能需要 LAG() 或 LEAD()。 @Charlieface 的上述答案给出了 LEAD()，这给出了 LAG()

LAG() 窗口函数可以在这种情况下使用。最好给出预期的输出，以便在发布之前测试结果。

SELECT Casekey
 , rnk
 , LAPayment
 , CASE WHEN LAG(LAPayment) over (order by Casekey)   is not null then  0 ELSE LAReserve END  AS LAReserve  
  FROM
  (SELECT 123456 AS Casekey
     , 1 as rnk
     , NULL AS LAPayment
     , 1080.00 AS LAReserve
    UNION ALL
   SELECT 123456 AS Casekey
      , 2 as rnk
      , 1080.00 AS LAPayment
      , null AS LAReserve
    UNION ALL
   SELECT 123456 AS Casekey
      , 3 as rnk
      , NULL AS LAPayment
      , NULL AS LAReserve
    ) AS A

【讨论】：