合并具有连续日期范围的记录

Question

我试图弄清楚如何将多条记录组合在一起，其中第一条记录的期限日期是另一条记录中生效日期的前一天。

以下是一些示例数据：

SELECT 1 AS MEM_ID, CAST('2017-01-01' AS DATE) AS EFF_DATE, CAST('2017-05-31' AS DATE) AS TERM_DATE
INTO #TEMP 
UNION 
SELECT 1 AS MEM_ID, CAST('2017-06-01' AS DATE) AS EFF_DATE, CAST('2018-01-31' AS DATE)
UNION 
SELECT 1 AS MEM_ID, CAST('2018-02-01' AS DATE) AS EFF_DATE, CAST('2018-06-30' AS DATE)
UNION 
SELECT 1 AS MEM_ID, CAST('2018-09-01' AS DATE) AS EFF_DATE, CAST('2078-12-31' AS DATE)
UNION 
SELECT 2 AS MEM_ID, CAST('2017-02-01' AS DATE) AS EFF_DATE, CAST('2017-04-30' AS DATE)
UNION 
SELECT 2 AS MEM_ID, CAST('2017-05-01' AS DATE) AS EFF_DATE, CAST('2018-03-31' AS DATE)
UNION 
SELECT 2 AS MEM_ID, CAST('2018-06-01' AS DATE) AS EFF_DATE, CAST('2018-06-30' AS DATE)
UNION 
SELECT 2 AS MEM_ID, CAST('2018-07-01' AS DATE) AS EFF_DATE, CAST('2078-12-31' AS DATE)
UNION 
SELECT 3 AS MEM_ID, CAST('2017-01-01' AS DATE) AS EFF_DATE, CAST('2017-10-31' AS DATE)
UNION 
SELECT 3 AS MEM_ID, CAST('2017-12-01' AS DATE) AS EFF_DATE, CAST('2018-03-31' AS DATE)
UNION 
SELECT 3 AS MEM_ID, CAST('2018-04-01' AS DATE) AS EFF_DATE, CAST('2018-06-30' AS DATE)
UNION 
SELECT 3 AS MEM_ID, CAST('2018-07-01' AS DATE) AS EFF_DATE, CAST('2078-12-31' AS DATE)

我创建了一个 CTE，它通过第二条记录的 DATE = DATE - 1 加入自身。不幸的是，它只结合了两条记录，我还没有弄清楚如何让它递归。

;WITH TEST AS (
SELECT DISTINCT MEM_ID,
    EFF_DATE,
    TERM_DATE, 
    ROW_NUMBER()OVER(ORDER BY MEM_ID, EFF_DATE) ROW_NUM
FROM #TEMP
)

SELECT * 
FROM TEST T 
INNER JOIN TEST T2 ON T.MEM_ID = T2.MEM_ID AND T.TERM_DATE = DATEADD(DAY, -1, T2.EFF_DATE)

这种方法的问题是，可能有三个或多个连续的记录需要合并为一个。

ID 1 应该有两条记录 - 一条来自 1/1/2017 - 6/30/2018，一条来自 9/1/2018 - 12/31/78。

ID 2 也应该有两条记录 - 2/1/2017 - 3/30/2018 和 6/1/2018 - 12/31/78。

ID 3 还应该有两条记录 - 1/1/2017 - 10/31/2017 和 12/1/2017 - 12/31/78。

如何合并这些记录？记录的开始日期主要是每月的第一天，学期日期的最后一天 - 我不需要担心异常值。

我研究了类似的问题，但他们只有两条记录需要合并并使用我使用的相同方法。

Answer 1

这是 LAG 和 LEAD 有用的类型。

;WITH CTE AS (SELECT DISTINCT  MEM_ID,
                  EFF_DATE,
                  LEAD(EFF_DATE, 1, NULL) OVER (PARTITION BY MEM_ID ORDER BY MEM_ID, EFF_DATE) AS TERM_DATE
              FROM #TEMP
             )

SELECT MEM_ID,
       EFF_DATE,
       TERM_DATE, 
       DATEADD(DAY, -1, TERM_DATE) AS D2
FROM CTE;

LEAD 基本上会在下一行出现峰值，并包括从该行中出现峰值的指定列。 LAG 执行上一行。