从表中选择连续范围

Question

我需要根据连续数字（N 列）和这些数字相关的相同“类别”（下面的 C 列）从表中提取连续范围。从图形上看，它看起来像这样：

 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

SQL Server 是 2005。谢谢。

Answer 1

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

Answer 2

RANK 函数比 ROW_NUMBER 更安全，以防任何 N 值重复，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;

Result，它正确地承受了重复的 4 和 10：

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

Answer 3

使用这个答案作为起始点，我最终得到以下结果：

;
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

Answer 4

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，
• 使用游标循环遍历包含按 N 排序的 N、C、D 的表中的条目，
• 使用变量检测新范围 (Ni < N(i-1)-1) 并存储 N1、N2， D1 和 D2
• 插入到检测到的每个范围的临时表中（检测到的新范围或光标的和）

请告诉我您是否需要代码示例。