如何找到前任的前任

Question

我正在尝试使用 SQL 查询来查找某个市镇的前身市镇，或者如果有的话，其他前身市镇。

这是我的输入表（MUNICIPALMERGE）：

city_id	有效年份	有效期至	predecessor_municipality_id
1000	1990	1995	空
1001	1996	2000	1000
1002	2001	2005	1001
1003	1990	2005	空

我的目标是一张表格，显示相应年份哪个城市有效。对于上面的例子，正确的表格如下：

年	city_id	valid_municipality_id
1990	1000	1000
1991	1000	1000
1992	1000	1000
1993	1000	1000
1994	1000	1000
1995	1000	1000
1996	1000	1001
1997	1000	1001
1998	1000	1001
1999	1000	1001
2000	1000	1001
2001	1000	1002
2002	1000	1002
2003	1000	1002
2004年	1000	1002
2005	1000	1002
1990	1001	1000
1991	1001	1000
1992	1001	1000
1993	1001	1000
1994	1001	1000
1995	1001	1000
1996	1001	1001
1997	1001	1001
1998	1001	1001
1999	1001	1001
2000	1001	1001
2001	1001	1002
2002	1001	1002
2003	1001	1002
2004年	1001	1002
2005	1001	1002
1990	1002	1000
1991	1002	1000
1992	1002	1000
1993	1002	1000
1994	1002	1000
1995	1002	1000
1996	1002	1001
1997	1002	1001
1998	1002	1001
1999	1002	1001
2000	1002	1001
2001	1002	1002
2002	1002	1002
2003	1002	1002
2004年	1002	1002
2005	1002	1002
1990	1003	1003
1991	1003	1003
1992	1003	1003
1993	1003	1003
1994	1003	1003
1995	1003	1003
1996	1003	1003
1997	1003	1003
1998	1003	1003
1999	1003	1003
2000	1003	1003
2001	1003	1003
2002	1003	1003
2003	1003	1003
2004年	1003	1003
2005	1003	1003

这意味着应为每个城市找到相应的前任或后继城市（如果有）。

这是否可能？如果可能，如何实现？

非常感谢您的帮助。

我尝试了下面的查询，但在 Valid_minicipality_id 列中得到了一些空值。

WITH
  YEARS AS
  (
    SELECT
      1990 AS YEAR
    UNION ALL
    SELECT
      YEAR+1
    FROM
      YEARS
    WHERE
      YEAR+1<=2005--YEAR(GETDATE())
  )
  --SELECT * FROM YEARS;
, YEARS_MUNICIPALITY AS
  (
    SELECT
      Y.YEAR
    , MM.MUNICIPALITY_ID
    , ISNULL(MM.PREDECESSOR_MUNICIPALITY_ID, MM.MUNICIPALITY_ID) AS PREDECESSOR_MUNICIPALITY_ID
    FROM
      YEARS Y
    INNER JOIN
      MUNICIPALMERGE MM
    ON
      Y.YEAR BETWEEN MM.VALID_YEAR_FROM AND MM.VALID_YEAR_TO
  )
  --SELECT * FROM YEARS_MUNICIPALITY;
, ALL_YEARS_MUNICIPALITY AS
  (
    SELECT
      Y.YEAR
    , MM.MUNICIPALITY_ID
    , MM.PREDECESSOR_MUNICIPALITY_ID
    FROM
      YEARS Y
    CROSS JOIN
      MUNICIPALMERGE MM
  )
--SELECT * FROM ALL_YEARS_MUNICIPALITY;
SELECT
  AYM.YEAR
, AYM.MUNICIPALITY_ID
, YM.MUNICIPALITY_ID AS VALID_MUNICIPALITY_ID
FROM
  ALL_YEARS_MUNICIPALITY AYM
LEFT JOIN
  YEARS_MUNICIPALITY YM
ON
  AYM.YEAR=YM.YEAR
AND AYM.MUNICIPALITY_ID=YM.PREDECESSOR_MUNICIPALITY_ID
ORDER BY
  AYM.MUNICIPALITY_ID
, AYM.YEAR;

Answer 1

我不太确定这是最有效的方法，但它确实做到了。

我使用

GENERATE_SERIES

来获取所有日历年，而不是 rCTE。如果您使用的不是 SQL Server 2022+，请使用计数。对于少量数据，rCTE 对于生成行来说“很好”，但它会变得慢快，因此我避免在所有情况下使用它们来生成此类数据，并使用基于集合的方法。

然后我使用 rCTE 来遍历数据的层次结构。然后，我使用进一步的 CTE 将值放在两侧（因此您有 1000,1001 和 1001,1000）并获得

DISTINCT

结果。

最后，我根据“有效”市镇的值，将其

JOIN

添加到您的原始数据中。结果如下：

CREATE TABLE dbo.YourTable (municipality_id int,
                            valid_year_from int,
                            valid_year_to int,
                            predecessor_municipality_id int);
GO

INSERT INTO dbo.YourTable (municipality_id,
                           valid_year_from,
                           valid_year_to,
                           predecessor_municipality_id)
VALUES (1000, 1990, 1995, NULL),
       (1001, 1996, 2000, 1000),
       (1002, 2001, 2005, 1001),
       (1003, 1990, 2005, NULL);
GO
WITH MinMaxYears AS(
    SELECT MIN(valid_year_from) AS MinYear,
           MAX(valid_year_to) AS MaxYear
    FROM dbo.YourTable),
Years AS(
    SELECT GS.value AS CalendarYear
    FROM MinMaxYears MMY
         CROSS APPLY GENERATE_SERIES(MMY.MinYear, MMY.MaxYear, 1) GS),
Municipalities AS(
    SELECT YT.municipality_id,
           YT.municipality_id AS Current_municipality_id,
           YT.predecessor_municipality_id
    FROM dbo.YourTable YT
    UNION ALL
    SELECT M.municipality_id,
           YT.municipality_id AS Current_municipality_id,
           YT.predecessor_municipality_id
    FROM dbo.YourTable YT
         JOIN Municipalities M ON YT.municipality_id = M.predecessor_municipality_id),
ValidMunicipalities AS(
    SELECT DISTINCT V.municipality_id,
                    V.valid_municipality_id
    FROM Municipalities M
         CROSS APPLY (VALUES(M.municipality_id, M.Current_municipality_id),
                            (M.Current_municipality_id, M.municipality_id))V(municipality_id,valid_municipality_id))
SELECT Y.CalendarYear,
       VM.municipality_id,
       VM.valid_municipality_id
FROM ValidMunicipalities VM
     CROSS JOIN Years Y
     JOIN dbo.YourTable YT ON Y.CalendarYear BETWEEN YT.valid_year_from AND YT.valid_year_to
                          AND VM.valid_municipality_id = YT.municipality_id
ORDER BY VM.municipality_id,
         VM.valid_municipality_id,
         Y.CalendarYear;
GO
DROP TABLE dbo.YourTable;