Oracle 11g Release 2

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create table data(amount, customer_number, groupid, seqf) as (
    select '1000+', 5555, 51, 2 from dual union all
    select '1000+', 5555, 52, 3 from dual union all
    select '1000+', 5555, 55, 4 from dual union all
    select '1000+', 5555, 56, 4 from dual union all
    select '1000+', 5555, 57, 4 from dual union all
    select '1000+', 5555, 60, 2 from dual union all
    select '1000+', 5555, 61, 4 from dual union all
    select '1000+', 5555, 65, 2 from dual union all
    select '1000+', 5555, 69, 2 from dual union all
    select '2000+', 6666, 55, 2 from dual );
10 rows affected

SELECT amount,
       customer_number,
       groupid,
       groupid + 6 AS max_groupid
FROM   (
  SELECT d.*,
         MIN( groupid )
           OVER ( PARTITION BY amount, customer_number )
           AS min_groupid,
         MIN( groupid )
           OVER (
             PARTITION BY amount, customer_number
             ORDER BY groupid
             RANGE BETWEEN 7 FOLLOWING AND UNBOUNDED FOLLOWING
           )
           AS next_groupid
  FROM   data d
)
START WITH groupid = min_groupid
CONNECT BY PRIOR amount          = amount
AND        PRIOR customer_number = customer_number
AND        PRIOR next_groupid    = groupid


AMOUNT
CUSTOMER_NUMBER
GROUPID
MAX_GROUPID


1000+
5555
51
57

1000+
5555
60
66

1000+
5555
69
75

2000+
6666
55
61


SELECT amount,
       customer_number,
       COUNT(*)
FROM   (
  SELECT d.*,
         MIN( groupid )
           OVER ( PARTITION BY amount, customer_number )
           AS min_groupid,
         MIN( groupid )
           OVER (
             PARTITION BY amount, customer_number
             ORDER BY groupid
             RANGE BETWEEN 7 FOLLOWING AND UNBOUNDED FOLLOWING
           )
           AS next_groupid
  FROM   data d
)
START WITH groupid = min_groupid
CONNECT BY PRIOR amount          = amount
AND        PRIOR customer_number = customer_number
AND        PRIOR next_groupid    = groupid
GROUP BY amount, customer_number


AMOUNT
CUSTOMER_NUMBER
COUNT(*)


1000+
5555
3

2000+
6666
1