Re: Flatten table using timestamp and source

On Friday 25 May 2012, Raj Mathur (राज माथुर) wrote:
> On Thursday 24 May 2012, Elrich Marx wrote:
> > If source changes, in this case from 1 to 2, then etime would be
> > the last value of stime for source =1; So for source 1 it starts
> > at stime 13:00 and continues till 13:02 (etime).
> >
> > This should result in 3 records, because source is 1, then 2, then
> > 1 again. I hope this explains ?
>
> I think I understand. Here's a partially working example -- it
> doesn't compute the last interval. Probably amenable to some severe
> optimisation too, but then I don't claim to be an SQL expert :)

With the last interval computation:

QUERY
-----
with
first_last as
(
select * from
(
select
source,
time,
case
when
lag(source) over (order by time) != source
or lag(source) over (order by time) is null
then 1 else 0
end as is_first,
case
when
lead(source) over (order by time) != source
or lead(source) over (order by time) is null
then 1 else 0
end as is_last
from
p
) foo
where
is_first != 0 or is_last != 0
)
select
t1.source,
start_time,
end_time
from
(
select
source,
time as start_time
from
first_last
where
is_first = 1
) t1
join
(
select
source,
time as end_time,
is_last
from
first_last
where
is_last = 1
) t2
on
(
t1.source = t2.source
and t2.end_time > t1.start_time
and
(
(
t2.end_time <
(
select
time
from
first_last
where
source != t2.source
and time > t1.start_time
order by
time
limit
1
)
)
or
(
t1.start_time =
(
select
time
from
first_last
where
is_first = 1
order by
time desc
limit
1
)
and t2.end_time =
(
select
time
from
first_last
where
is_last = 1
order by
time desc
limit
1
)
)
)
)
;

RESULT (with same data set as before)
------
source | start_time | end_time
--------+---------------------+---------------------
1 | 1970-01-01 05:30:01 | 1970-01-01 05:32:01
6 | 1970-01-01 05:33:01 | 1970-01-01 05:37:01
2 | 1970-01-01 05:38:01 | 1970-01-01 05:41:01
6 | 1970-01-01 05:42:01 | 1970-01-01 05:46:01
4 | 1970-01-01 05:47:01 | 1970-01-01 05:51:01
0 | 1970-01-01 05:52:01 | 1970-01-01 05:55:01
7 | 1970-01-01 05:56:01 | 1970-01-01 05:58:01
8 | 1970-01-01 05:59:01 | 1970-01-01 06:03:01
1 | 1970-01-01 06:04:01 | 1970-01-01 06:10:01
8 | 1970-01-01 06:11:01 | 1970-01-01 06:13:01
6 | 1970-01-01 06:14:01 | 1970-01-01 06:16:01
4 | 1970-01-01 06:17:01 | 1970-01-01 06:18:01
9 | 1970-01-01 06:19:01 | 1970-01-01 06:22:01
2 | 1970-01-01 06:23:01 | 1970-01-01 06:25:01
1 | 1970-01-01 06:26:01 | 1970-01-01 06:29:01
4 | 1970-01-01 06:30:01 | 1970-01-01 06:34:01
0 | 1970-01-01 06:35:01 | 1970-01-01 06:37:01
9 | 1970-01-01 06:38:01 | 1970-01-01 06:42:01
1 | 1970-01-01 06:43:01 | 1970-01-01 06:45:01
8 | 1970-01-01 06:46:01 | 1970-01-01 06:50:01
0 | 1970-01-01 06:51:01 | 1970-01-01 06:57:01
2 | 1970-01-01 06:58:01 | 1970-01-01 07:05:01
4 | 1970-01-01 07:06:01 | 1970-01-01 07:07:01
2 | 1970-01-01 07:08:01 | 1970-01-01 07:12:01
7 | 1970-01-01 07:13:01 | 1970-01-01 07:14:01
9 | 1970-01-01 07:15:01 | 1970-01-01 07:17:01
7 | 1970-01-01 07:18:01 | 1970-01-01 07:21:01

Would be interested in seeing how to shorten and/or optimise this query.

Regards,

-- Raj
--
Raj Mathur || raju(at)kandalaya(dot)org || GPG:
http://otheronepercent.blogspot.com || http://kandalaya.org || CC68
It is the mind that moves || http://schizoid.in || D17F