Sql 在一个字段更改时查找开始和结束日期

我在一张表格里有这些数据

FIELD_A   FIELD_B     FIELD_D
249052903   10/15/2011 N
249052903   11/15/2011 P ------------- VALUE CHANGED
249052903   12/15/2011 P
249052903   1/15/2012   N ------------- VALUE CHANGED
249052903   2/15/2012   N
249052903   3/15/2012   N
249052903   4/15/2012   N
249052903   5/15/2012   N
249052903   6/15/2012   N
249052903   7/15/2012   N
249052903   8/15/2012   N
249052903   9/15/2012   N

当字段_D中的值发生变化时，它会形成一个组，我需要该组中的最小和最大日期。查询应该返回

FIELD_A   GROUP_START   GROUP_END
249052903   10/15/2011  10/15/2011
249052903   11/15/2011  12/15/2011
249052903   1/15/2012              9/15/2012

到目前为止，我所看到的例子中，字段D中的数据是独一无二的。这里的数据可以重复显示，首先是N，然后变为P，然后变回N

任何帮助都将不胜感激

---

感谢您不要使用SQL来解决此问题，因为在SQL中，单表扫描是不可能的，因为它需要记录之间的比较。它需要一个完整的表扫描，再加上至少一个自身的连接。用命令式语言实现解决方案很简单，只需要一次表扫描。

---

编辑：最好是存储过程。

使用子查询在SQL中很容易表达这一点：

select Field_A, Field_D, min(Field_B) as Group_Start, max(Field_B) as Group_End
from (select t.*,
             (select min(field_B)
              from t t2
              where t2.field_A = t.field_A and
                    t2.field_B > t.field_B and
                    t2.Field_D <> t.field_D
             ) as TheGroup
      from t
     ) t
group by Field_A, Field_D, TheGroup

这是使用相关子查询分配组标识符。标识符是字段_D更改的字段_B的第一个值

---

您没有提到您正在使用的数据库，因此它使用标准SQL。

您可以使用分析函数-滞后、超前和累加，如果SQL实现支持它们，它们将发挥您的优势。SQL小提琴

---

我对答案做了一些修改，你有多个字段。这应该始终有效：-

WITH EndsMarked 
AS 
(
    SELECT 

         [Field_A]
        ,[Field_B]
        ,CASE 
            WHEN LAG([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) IS NULL
             AND ROW_NUMBER() OVER (PARTITION BY [Field_A] ORDER BY [Field_B]) = 1 
            THEN 1
            WHEN LAG([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) > 0
              <> LAG([Field_D],0) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) > 0
            THEN 1 
            ELSE 0 
        END AS IS_START
       ,CASE 
            WHEN LEAD([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) IS NULL
             AND ROW_NUMBER() OVER (PARTITION BY [Field_A] ORDER BY [Field_B] DESC) = 1 
            THEN 1
            WHEN LEAD([Field_D],0) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) 
              <> LEAD([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) 
            THEN 1          
            ELSE 0 
        END                 AS IS_END

    FROM 
    (
        SELECT

            [Field_A]
           ,[Field_B]
           ,[Field_D]
           ,[Aantal Facturen]

        FROM [T]

    )   F
    
)
,GroupsNumbered 
AS 
(
  SELECT
     [Field_A]
    ,[Field_B]
    ,IS_START
    ,IS_END
    ,COUNT(CASE
               WHEN IS_START = 1 
               THEN 1 
           END)                     OVER (ORDER BY [Field_A]
                                                  ,[Field_B]) AS GroupNum
  FROM      EndsMarked
  WHERE     IS_START        = 1 
     OR     IS_END          = 1
)

    SELECT

        [Field_A]
        ,MIN([Field_B]) AS GROUP_START
        ,MAX([Field_B]) AS GROUP_END

    FROM GroupsNumbered

    GROUP BY [Field_A], GroupNum

---

此查询仅创建两个组。该组需要附加条件t2.Field_B>t.Field_B。我仍然认为存储过程将是一种更快、更易于维护的解决方案。@koriander。感谢你指出我遗漏了字段B上的条件。不过，我不同意你其余的评论。我实际上喜欢你SQL查询的优雅。但如果性能是个问题，我肯定会研究基本的顺序文件处理。原始数据看起来像来自日志，自然排序，不需要索引。这种说法完全错误。SQL中的表本质上是无序的。为了以正确的顺序检索adta，您需要使用order by子句，这需要多次读取/写入数据。根据理论关系模型，关系是无序的。但是，实际上，可以使用聚集索引按顺序存储表，请参阅。此外，解决此问题的SQL将使用多个索引，order_by需要一个索引。每个索引只需要读取一次表本身，而不是像您声称的那样多次。事实上，仅就这个问题而言，将此表存储为单个顺序文件（而不是存储在DBMS中）似乎是最好的解决方案。感谢您的回答，但是这不会产生正确的答案，因为只返回一行。EndsMarked只创建一个组。您是否运行了SQL FIDLE？查询返回三行-正是您所说的查询应该返回的三行。感谢您的后续操作。这是我的错误。查询返回了正确的数据。谢谢你的帮助。

WITH EndsMarked 
AS 
(
    SELECT 

         [Field_A]
        ,[Field_B]
        ,CASE 
            WHEN LAG([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) IS NULL
             AND ROW_NUMBER() OVER (PARTITION BY [Field_A] ORDER BY [Field_B]) = 1 
            THEN 1
            WHEN LAG([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) > 0
              <> LAG([Field_D],0) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) > 0
            THEN 1 
            ELSE 0 
        END AS IS_START
       ,CASE 
            WHEN LEAD([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) IS NULL
             AND ROW_NUMBER() OVER (PARTITION BY [Field_A] ORDER BY [Field_B] DESC) = 1 
            THEN 1
            WHEN LEAD([Field_D],0) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) 
              <> LEAD([Field_D],1) OVER (PARTITION BY [Field_A] ORDER BY [Field_A],[Field_B]) 
            THEN 1          
            ELSE 0 
        END                 AS IS_END

    FROM 
    (
        SELECT

            [Field_A]
           ,[Field_B]
           ,[Field_D]
           ,[Aantal Facturen]

        FROM [T]

    )   F
    
)
,GroupsNumbered 
AS 
(
  SELECT
     [Field_A]
    ,[Field_B]
    ,IS_START
    ,IS_END
    ,COUNT(CASE
               WHEN IS_START = 1 
               THEN 1 
           END)                     OVER (ORDER BY [Field_A]
                                                  ,[Field_B]) AS GroupNum
  FROM      EndsMarked
  WHERE     IS_START        = 1 
     OR     IS_END          = 1
)

    SELECT

        [Field_A]
        ,MIN([Field_B]) AS GROUP_START
        ,MAX([Field_B]) AS GROUP_END

    FROM GroupsNumbered

    GROUP BY [Field_A], GroupNum