Grouping by Date inclusivity - sql

Question

Here is the data I'm working with here
Accountid
Month
123
08/01/2021
123
09/01/2021
123
03/01/2022
123
04/01/2022
123
05/01/2022
123
06/01/2022
I'm trying to insert into a new table where the data is like this
Accountid
Start Month
End Month
123
08/01/2021
09/01/2021
123
03/01/2022
06/01/2022
I'm not sure how to separate them with the gap, and group by the account id in this case.
Thanks in advance

Answer 1

In 12c+ you may also use match_recognize for gaps-and-islands problems to define grouping rules (islands) in a more readable and natural way.
select *
from input_
match_recognize(
partition by accountid
order by month asc
measures
first(month) as start_month,
last(month) as end_month
/*Any month followed by any number of subsequent month */
pattern(any_ next*)
define
/*Next is the month right after the previous one*/
next as months_between(month, prev(month)) = 1
)
ACCOUNTID
START_MONTH
END_MONTH
123
2021-08-01
2021-09-01
123
2022-03-01
2022-06-01
db<>fiddle here

Answer 2

That's a gaps and islands problem; one option to do it is:
Sample data:
SQL> with test (accountid, month) as
2 (select 123, date '2021-01-08' from dual union all
3 select 123, date '2021-01-09' from dual union all
4 select 123, date '2021-01-03' from dual union all
5 select 123, date '2021-01-04' from dual union all
6 select 123, date '2021-01-05' from dual union all
7 select 123, date '2021-01-06' from dual
8 ),
Query begins here:
9 temp as
10 (select accountid, month,
11 to_char(month, 'J') - row_number() Over
12 (partition by accountid order by month) diff
13 from test
14 )
15 select accountid,
16 min(month) as start_month,
17 max(month) as end_Month
18 from temp
19 group by accountid, diff
20 order by accountid, start_month;
ACCOUNTID START_MONT END_MONTH
---------- ---------- ----------
123 03/01/2021 06/01/2021
123 08/01/2021 09/01/2021
SQL>
Although related to MS SQL Server, have a look at Introduction to Gaps and Islands Analysis; should be interesting reading for you, I presume.