如何使用 CTE 来比较值

Question

我需要根据以前的记录返回 0 或 1。示例表：

DECLARE @x TABLE(ProductID INT, Failed bit, SampleDate date, LevelCode int);
INSERT @x VALUES
(101, 0, '20151201', 1),    
(101, 1, '20151205', 2),    
(101, 0, '20151206', 3),
(101, 1, '20151208', 2), 
(102, 1, '20151202', 1),
(102, 0, '20151204', 2),    
(102, 0, '20151205', 3),
(103, 0, '20160101', 1),
(103, 1, '20160102', 2),
(103, 0, '20160103', 2),
(104, 0, '20160101', 1),
(104, 0, '20160102', 2),
(104, 0, '20160103', 3);

我们在最后一条记录上唯一关心的是LevelCode（即每个ProductID 的最后一条记录）。最后一条记录是否通过/失败无关紧要。然后，我们查看该 ProductID 的所有其他记录（因此是最后一条记录之前的所有记录），如果出现与最后一条记录相同的 LevelCode 失败，我们将 IsLastRunSameLevelAsPreviousRun 设置为 1，否则为 0：

 ProductID     IsLastRunSameLevelAsPreviousRun
 101           1
 102           0
 103           1
 104           0

如果有一个没有失败ProductID的IsLastRunSameLevelAsPreviousRun应该返回0。

非常感谢任何帮助或提示。

Answer 1

使用LAG，您无需任何连接即可实现目标：

WITH cte AS
  (
    SELECT
      ProductID,
      SampleDate,
      MaxSampleDate = MAX(SampleDate) OVER (PARTITION BY ProductID),
      PrevFailed    = LAG(Failed, 1, 0) OVER (PARTITION BY ProductID, LevelCode
                                              ORDER BY SampleDate)
    FROM
      @x
  )
SELECT
  ProductID,
  IsLastRunSameLevelAsPreviousRun = PrevFailed
FROM
  cte
WHERE
  SampleDate = MaxSampleDate
;

在cte获得先前的Failed为相同的状态LevelCode针对每个内的每个行ProductID组，返回0时不存在匹配的行。它还计算每个组中的最后日期，以便稍后使用它来确定组中的最后一行。

这是它返回的内容：

ProductID  SampleDate  MaxSampleDate  PrevFailed
---------  ----------  -------------  ----------
101        2015-12-01  2015-12-08     0
101        2015-12-05  2015-12-08     0
101        2015-12-08  2015-12-08     1
101        2015-12-06  2015-12-08     0
102        2015-12-02  2015-12-05     0
102        2015-12-04  2015-12-05     0
102        2015-12-05  2015-12-05     0
103        2016-01-01  2016-01-03     0
103        2016-01-02  2016-01-03     0
103        2016-01-03  2016-01-03     1
104        2016-01-01  2016-01-03     0
104        2016-01-02  2016-01-03     0
104        2016-01-03  2016-01-03     0

主要选择在使用基本上只是需要每个组的最后一排SampleDate = MaxSampleDate过滤器，只拉ProductID和PrevFailed也改名后者IsLastRunSameLevelAsPreviousRun，使最终输出变成你想要的东西：

ProductID  IsLastRunSameLevelAsPreviousRun
---------  -------------------------------
101        1
102        0
103        1
104        0

Answer 2

一种方法是使用ROW_NUMBER两次。

首先对由ProductID( CTE_RowNumbersAll)分区的表的所有行进行编号，并仅获取每个ProductID( CTE_LastAll)的最后一行。

然后编号所有失败的行 ( CTE_RowNumbersFailed) 并获取每个失败的行ProductID( CTE_LastFailed)。

最后将LEFT JOIN中间结果放在一起并用于CASE比较LevelCode值。

更新

根据您的最后一条评论，我更改了查询。CTE_RowNumbersFailed现在基于CTE_RowNumbersAll并且有一个额外的过滤器rnAll > 1可以从考虑中删除最后一行。

WITH
CTE_RowNumbersAll
AS
(
    SELECT
        ProductID
        ,Failed
        ,SampleDate
        ,LevelCode
        ,ROW_NUMBER() OVER(PARTITION BY ProductID ORDER BY SampleDate DESC) AS rnAll
    FROM @x
)
,CTE_LastAll
AS
(
    SELECT
        ProductID
        ,LevelCode
    FROM CTE_RowNumbersAll
    WHERE rnAll = 1
)
,CTE_RowNumbersFailed
AS
(
    SELECT
        ProductID
        ,Failed
        ,SampleDate
        ,LevelCode
        ,ROW_NUMBER() OVER(PARTITION BY ProductID ORDER BY SampleDate DESC) AS rnFailed
    FROM CTE_RowNumbersAll
    WHERE
        Failed = 1
        AND rnAll > 1
)
,CTE_LastFailed
AS
(
    SELECT
        ProductID
        ,LevelCode
    FROM CTE_RowNumbersFailed
    WHERE rnFailed = 1
)
SELECT
    CTE_LastAll.ProductID
    ,CASE WHEN CTE_LastAll.LevelCode = CTE_LastFailed.LevelCode 
        THEN 1 ELSE 0 END AS IsLastRunSameLevelAsPreviousRun
FROM
    CTE_LastAll
    LEFT JOIN CTE_LastFailed ON CTE_LastFailed.ProductID = CTE_LastAll.ProductID
ORDER BY CTE_LastAll.ProductID;

结果

+-----------+---------------------------------+
| ProductID | IsLastRunSameLevelAsPreviousRun |
+-----------+---------------------------------+
|       101 |                               1 |
|       102 |                               0 |
|       103 |                               1 |
|       104 |                               0 |
+-----------+---------------------------------+