sql-server - MS SQL 2012：查找数字序列

Question

我有一张这样的桌子：

    WITH S AS (
    SELECT 'B' type, 1 number
UNION SELECT 'B', 2
UNION SELECT 'B', 3
UNION SELECT 'B', 4
UNION SELECT 'B', 5
UNION SELECT 'A', 6
UNION SELECT 'A', 7
UNION SELECT 'B', 8
UNION SELECT 'B', 9
UNION SELECT 'B', 10
UNION SELECT 'C', 11
UNION SELECT 'A', 12
UNION SELECT 'B', 13
UNION SELECT 'B', 14
UNION SELECT 'B', 15
UNION SELECT 'B', 16
UNION SELECT 'B', 17
UNION SELECT 'A', 18
UNION SELECT 'C', 19
UNION SELECT 'B', 20
UNION SELECT 'B', 21
    ) 

如何获得每种类型连续出现的独特数字序列（例如，3 个或更多）？例如对于 B 1~5 会有类似'B1'，对于 B 8~10 -'B2'等。我怀疑应该有类似的组合LEAD/LAGand DENSE_RANK()，但不知道如何申请。数字是唯一的，如果这很重要的话。

结果应如下所示：

Type   Number  Sequence
-----------------------
B        1        B1
B        2        B1
B        3        B1
B        4        B1
B        5        B1
A        6        NULL
......................
B        8        B2
B        9        B2
B        10       B2
C        11       NULL
A        12       NULL
B        13       B3
....................
B        17       B3

Answer 1

一种方法是使用行号DENSE_RANK()的组合和差异。

WITH S AS (
    SELECT 'B' type, 1 number
UNION SELECT 'B', 2
UNION SELECT 'B', 3
UNION SELECT 'B', 4
UNION SELECT 'B', 5
UNION SELECT 'A', 6
UNION SELECT 'A', 7
UNION SELECT 'B', 8
UNION SELECT 'B', 9
UNION SELECT 'B', 10
UNION SELECT 'C', 11
UNION SELECT 'A', 12
UNION SELECT 'B', 13
UNION SELECT 'B', 14
UNION SELECT 'B', 15
UNION SELECT 'B', 16
UNION SELECT 'B', 17
UNION SELECT 'A', 18
UNION SELECT 'C', 19
UNION SELECT 'B', 20
UNION SELECT 'B', 21
    ) 
SELECT type, 
       number, 
       sequence = CASE 
            WHEN type = 'B' 
            THEN 'B' + CAST(DENSE_RANK() OVER (ORDER BY CASE WHEN type = 'B' THEN 0 ELSE 1 END, RN) AS VARCHAR(10)) 
            END
FROM (
    SELECT *, RN = ROW_NUMBER() OVER (ORDER BY number) - ROW_NUMBER() OVER (PARTITION BY type ORDER BY number)
    FROM S
    ) AS T
ORDER BY number;

Answer 2

有一个回复，仅仅几分钟，它包含了我想要的确切解决方案（其余的我可以弄清楚）：

SELECT type, R1 = min(number), R2 = max(number) FROM (
SELECT *, number - ROW_NUMBER() OVER (PARTITION BY type ORDER BY number) Grp From S
) A
GROUP BY type

无法评价答案 - 那时它已经被删除了。解决方案是寻找“差距和岛屿”——现在我知道了。