Sql 从表中选择连续范围

我需要根据连续的数字（N列）和这些数字所涉及的相同“类别”（下面的C列），从表中提取连续的范围。从图形上看，它如下所示：

 N  C  D
--------
 1  x  a           C  N1  N2  D1  D2
 2  x  b          ------------------
 3  x  c           x   1   4   a   d     (continuous range with same N)
 4  x  d    ==>    x   6   7   e   f     (new range because "5" is missing)
 6  x  e           y   8  10   g   h     (new range because C changed to "y")
 7  x  f
 8  y  g
 9  y  h
10  y  i

---

SQLServer是2005年的。谢谢。

编写一个存储过程。它将创建并填充一个包含C、N1、N2、D1和D2列的临时表

• 创建临时表
• 使用光标循环表中的条目，这些条目包含按N排序的N、C、D
• 使用变量检测新范围（Ni
• 针对每个检测到的范围（检测到的新范围或光标的和）插入临时表

如果需要代码示例，请告诉我

DECLARE @myTable Table
(
    N INT,
    C CHAR(1),
    D CHAR(1)
)
INSERT INTO @myTable(N,C,D) VALUES(1,  'x', 'a');
INSERT INTO @myTable(N,C,D) VALUES(2,  'x', 'b');
INSERT INTO @myTable(N,C,D) VALUES(3,  'x', 'c');
INSERT INTO @myTable(N,C,D) VALUES(4,  'x', 'd');
INSERT INTO @myTable(N,C,D) VALUES(6,  'x', 'e');
INSERT INTO @myTable(N,C,D) VALUES(7,  'x', 'f');
INSERT INTO @myTable(N,C,D) VALUES(8,  'y', 'g');
INSERT INTO @myTable(N,C,D) VALUES(9,  'y', 'h');
INSERT INTO @myTable(N,C,D) VALUES(10, 'y', 'i');


WITH StartingPoints AS(

    SELECT A.*, ROW_NUMBER() OVER(ORDER BY A.N) AS rownum
    FROM @myTable AS A
    WHERE NOT EXISTS(
        SELECT *
        FROM @myTable B
        WHERE B.C = A.C
          AND B.N = A.N - 1
    )
 ),
 EndingPoints AS(
    SELECT A.*, ROW_NUMBER() OVER(ORDER BY A.N) AS rownum
    FROM @myTable AS A
    WHERE NOT EXISTS (
        SELECT *
        FROM @myTable B
        WHERE B.C = A.C
          AND B.N = A.N + 1
    )
 ) 
SELECT StartingPoints.C,
       StartingPoints.N AS [N1],
       EndingPoints.N AS [N2],
       StartingPoints.D AS [D1],
       EndingPoints.D AS [D2] 
FROM StartingPoints
JOIN EndingPoints ON StartingPoints.rownum = EndingPoints.rownum

结果：

C    N1          N2          D1   D2
---- ----------- ----------- ---- ----
x    1           4           a    d
x    6           7           e    f
y    8           10          g    i

---

在任何N个值重复的情况下，RANK函数比ROW_NUMBER更安全，如下例所示：

declare @ncd table(N int, C char, D char);

insert into @ncd
select 1,'x','a' union all
select 2,'x','b' union all
select 3,'x','c' union all
select 4,'x','d' union all
select 4,'x','e' union all
select 7,'x','f' union all
select 8,'y','g' union all
select 9,'y','h' union all
select 10,'y','i' union all
select 10,'y','j';

with a as (
    select *
    , r = N-rank()over(partition by C order by N)
    from @ncd
)
select C=MIN(C)
, N1=MIN(N)
, N2=MAX(N)
, D1=MIN(D)
, D2=MAX(D)
from a
group by r;

正确承受重复4和10的结果：

C    N1          N2          D1   D2
---- ----------- ----------- ---- ----
x    1           4           a    e
x    7           7           f    f
y    8           10          g    j

作为起点，我得出以下结论：

;
WITH data (N, C, D) AS (
  SELECT 1,  'x', 'a' UNION ALL
  SELECT 2,  'x', 'b' UNION ALL
  SELECT 3,  'x', 'c' UNION ALL
  SELECT 4,  'x', 'd' UNION ALL
  SELECT 6,  'x', 'e' UNION ALL
  SELECT 7,  'x', 'f' UNION ALL
  SELECT 8,  'y', 'g' UNION ALL
  SELECT 9,  'y', 'h' UNION ALL
  SELECT 10, 'y', 'i'
),
ranked AS (
  SELECT
    curr.*,
    Grp     = curr.N - ROW_NUMBER() OVER (PARTITION BY curr.C ORDER BY curr.N),
    IsStart = CASE WHEN pred.C IS NULL THEN 1 ELSE 0 END,
    IsEnd   = CASE WHEN succ.C IS NULL THEN 1 ELSE 0 END
  FROM data AS curr
    LEFT JOIN data AS pred ON curr.C = pred.C AND curr.N = pred.N + 1
    LEFT JOIN data AS succ ON curr.C = succ.C AND curr.N = succ.N - 1
)
SELECT
  C,
  N1 = MIN(N),
  N2 = MAX(N),
  D1 = MAX(CASE IsStart WHEN 1 THEN D END),
  D2 = MAX(CASE IsEnd   WHEN 1 THEN D END)
FROM ranked
WHERE 1 IN (IsStart, IsEnd)
GROUP BY C, Grp

---

通过存储过程执行此操作是否可以接受？如果您可以访问SQL Cookbook，这是recipe 10.3。太复杂了。@MattFenwick:谢谢，看来在我仔细考虑之后，recepie可以做我需要的事情。谢谢，我会把代码写出来的。我希望非光标解决方案。源表可能有数百万行长。