Oracle SQL中的序列号

Question

Hi I have my table data as below.

Year    Period  Start_Date  End_Date
2019    6   1-Jun-19    30-Jun-19
2019    7   1-Jul-19    31-Jul-19

I want to fetch the data as below based on above.

hear period end date will be the Fridays between start_date and End_date in the above table.

Period  Sequence_no Period_end_dt
6        1           07-Jun-19
6        2           14-Jun-19
6        3           21-Jun-19
6        4           28-Jun-19
7        1           05-Jul-19
7        2           12-Jul-19
7        3           19-Jul-19
7        4           26-Jul-19

Answer 1

You can use a recursive CTE:

with cte(year, sequence_no, period_end_dt, end_dt) as (
      select year, period, 1 as sequence_no, start_date + 6 as period_end_dt, end_dt
      from t
      union all
      select year, period, sequence_no + 1, period_end_dt + 7 as period_end_dt, end_dt
      from t
      where period_end_dt + 7 < end_dt
     )
select year, period, sequence_no, period_end_dt
from t;

Answer 2

Another recursive CTE (11gR2+):

with rcte (year, period, end_date, sequence_no, period_end_dt) as (
  select year, period, end_date, 1, next_day(start_date - 1, 'Friday')
  from your_table
  union all
  select year, period, end_date, sequence_no + 1, period_end_dt + 7
  from rcte
  where period_end_dt + 7 < end_date
)
select year, period, sequence_no, period_end_dt
from rcte
order by year, period, sequence_no;

      YEAR     PERIOD SEQUENCE_NO PERIOD_END
---------- ---------- ----------- ----------
      2019          6           1 2019-06-07
      2019          6           2 2019-06-14
      2019          6           3 2019-06-21
      2019          6           4 2019-06-28
      2019          7           1 2019-07-05
      2019          7           2 2019-07-12
      2019          7           3 2019-07-19
      2019          7           4 2019-07-26

The next_day() is passed the day before the start day, in case the start is actually a Friday. The downside is that the day name has to be passed int he session date language, and that can't be overridden as part of the function call. If that isn't acceptable you can manipulate the date using ISO weekday numbers, but it's a bit more work.

with rcte (year, period, end_date, sequence_no, period_end_dt) as (
  select year, period, end_date, 1, trunc(start_date + 2, 'IW') + 4
  from your_table
  union all
  select year, period, end_date, sequence_no + 1, period_end_dt + 7
  from rcte
  where period_end_dt + 7 < end_date
)
select year, period, sequence_no, period_end_dt
from rcte
order by year, period, sequence_no;

      YEAR     PERIOD SEQUENCE_NO PERIOD_END
---------- ---------- ----------- ----------
      2019          6           1 2019-06-07
      2019          6           2 2019-06-14
      2019          6           3 2019-06-21
      2019          6           4 2019-06-28
      2019          7           1 2019-07-05
      2019          7           2 2019-07-12
      2019          7           3 2019-07-19
      2019          7           4 2019-07-26

db<>fiddle