在Oracle中字段值更改时增加行号

我需要帮助在Oracle中编写查询以获取以下数据.数据按人员和日期字段排序.

Person     Day   Flag
    ------     ---   ---- 
    person1    day1   Y
    person1    day2   Y
    person1    day3   Y
    person1    day4   N
    person1    day5   N
    person1    day6   Y
    person1    day7   Y
    person1    day8   Y

我需要有一个Group_Number列,只要Flag值发生变化就会增加.我的结果应如下所示

Person     Day   Flag  Group_Number
    ------     ---   ----  ------------
    person1    day1   Y    1
    person1    day2   Y    1
    person1    day3   Y    1
    person1    day4   N    2
    person1    day5   N    2
    person1    day6   Y    3
    person1    day7   Y    3
    person1    day8   Y    3

我认为有办法使用分析函数,如ROW_NUMBER,LEAD等获得上述结果.

SQL> WITH data AS (
  2            SELECT 'person1' person,'day1' day,'Y' flag FROM dual
  3  UNION ALL SELECT 'person1' person,'day2' day,'Y' flag FROM dual
  4  UNION ALL SELECT 'person1' person,'day3' day,'Y' flag FROM dual
  5  UNION ALL SELECT 'person1' person,'day4' day,'N' flag FROM dual
  6  UNION ALL SELECT 'person1' person,'day5' day,'N' flag FROM dual
  7  UNION ALL SELECT 'person1' person,'day6' day,'Y' flag FROM dual
  8  UNION ALL SELECT 'person1' person,'day7' day,'Y' flag FROM dual
  9  UNION ALL SELECT 'person1' person,'day8' day,'Y' flag FROM dual
 10  )
 11  SELECT person,DAY,flag,SUM(gap) over (PARTITION BY person
 12                                           ORDER BY DAY) grp
 13    FROM (SELECT person,14                 CASE WHEN flag = lag(flag) over (PARTITION BY person
 15                                                  ORDER BY DAY)
 16                      THEN 0
 17                      ELSE 1
 18                 END gap
 19            FROM DATA);

PERSON  DAY  FLAG        GRP
------- ---- ---- ----------
person1 day1 Y             1
person1 day2 Y             1
person1 day3 Y             1
person1 day4 N             2
person1 day5 N             2
person1 day6 Y             3
person1 day7 Y             3
person1 day8 Y             3

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