Oracle SQL query to group consecutive records - sql

Question

I've imported data ("Amount" and "Narration") from a spreadsheet into a table and need help with a query to group consecutive records according to their "Narration", for example:
Expected output:
line_no amount narration calc_group <-Not part of table
----------------------------------------
1 10 Reason 1 1
2 -10 Reason 1 1
3 5 Reason 2 2
4 5 Reason 2 2
5 -10 Reason 2 2
6 -8 Reason 1 3
7 8 Reason 1 3
8 11 Reason 1 3
9 99 Reason 3 4
10 -99 Reason 3 4
I've tried some analytical functions:
select line_no, amount, narration,
first_value (line_no) over
(partition by narration order by line_no) "calc_group"
from test
order by line_no
But that does not work because the Narration of line 6 to 8 is the same as line 1 and 2.
line_no amount narration calc_group
----------------------------------------
1 10 Reason 1 1
2 -10 Reason 1 1
3 5 Reason 2 3
4 5 Reason 2 3
5 -10 Reason 2 3
6 -8 Reason 1 1
7 8 Reason 1 1
8 11 Reason 1 1
9 99 Reason 3 4
10 -99 Reason 3 4
UPDATE
I've managed to do it using lag analytical function and sequences, not very elegant but it works. There should be a better way, please comment!
create or replace function get_next_test_seq
return number
as
begin
return test_seq.nextval;
end get_next_test_seq;
create or replace function get_curr_test_seq
return number
as
begin
return test_seq.currval;
end get_curr_test_seq;
update test
set group_no =
(with cte1
as (select line_no, amount, narration,
lag (narration) over (order by line_no) prev_narration, group_no
from test
order by line_no),
cte2
as (select line_no, amount, narration, group_no,
case when prev_narration is null or prev_narration <> narration then get_next_test_seq else get_curr_test_seq end new_group_no
from cte1)
select new_group_no
from cte2
where cte2.line_no = test.line_no);
UPDATE 2
I'm satisfied with the better accepted answer. Thanks kordiko!

Answer 1

Try this query:
SELECT line_no,
amount,
narration,
SUM( x ) OVER ( ORDER BY line_no
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
) as calc_group
FROM (
SELECT t.*,
CASE lag( narration ) OVER (order by line_no )
WHEN narration THEN 0
ELSE 1 END x
FROM test t
)
ORDER BY line_no
demo --> http://www.sqlfiddle.com/#!4/6d7aa/9