Split a query in date-ranges

Question

DB version 10g
a sample table is
my tab
(dt date,
status varchar2(2))
status in ('M','L','H') (medium,low,high)
sample data are: (date in 'dd-mm-yyy hh24Mi:ss' format)
DT STATUS
02-03-2006 08:16:00 H
02-03-2006 08:20:11 H
02-03-2006 08:22:00 H
02-03-2006 08:23:22 H
02-03-2006 08:24:33 M
02-03-2006 08:25:44 H
02-03-2006 08:26:55 L
02-03-2006 14:27:59 L
03-03-2006 00:00:00 L
I'm interested in find duration for every status:
status H
from 02-03-2006 08:16:00 to 02-03-2006 08:24:33 => duration 8 min 33 secs;
from 02-03-2006 08:25:44 to 02-03-2006 08:26:55 => duration 1 min 11 secs;
status M
from 02-03-2006 08:24:33 to 02-03-2006 08:26:55 => duration 1 min 11 secs;
status L
from 02-03-2006 08:26:55 to 03-03-2006 00:00:00 => duration 15 h ....
there are a complex query for this purpose without using a procedure that scan all records to find the chenges of status?

Answer 1

Not very elegant:
SQL> select * from my_tab;
DT                  ST
02-03-2006 08:16:00 H
02-03-2006 08:20:11 H
02-03-2006 08:22:00 H
02-03-2006 08:23:22 H
02-03-2006 08:24:33 M
02-03-2006 08:25:44 H
02-03-2006 08:26:55 L
02-03-2006 14:27:59 L
8 rows selected.
SQL> select status, min(dt), max(ld) from (
  2  select status, dt,
  3  case when lead(dt) over(order by dt) is null then
  4  trunc(dt) + 1 else lead(dt) over(order by dt) end ld,
  5  (row_number() over(order by dt) -
  6  row_number() over(partition by status order by dt)) gr
  7  from my_tab
  8  ) group by status, gr
  9  /
ST MIN(DT)             MAX(LD)
H  02-03-2006 08:16:00 02-03-2006 08:24:33
H  02-03-2006 08:25:44 02-03-2006 08:26:55
L  02-03-2006 08:26:55 03-03-2006 00:00:00
M  02-03-2006 08:24:33 02-03-2006 08:25:44Probably a mistake in M example - if I interpret your question right,
M has to be from 02-03-2006 08:24:33 to the next "H" e.g. 2006 08:25:44 ?
Rgds.