Query Based on Date & Time Range

Question

Hello Users,
There is a requirement to display weekly report from saturday 8:00 AM to previous saturday 08:00 AM.
I have a table "Downtime"
IPADDRESS       First Occurrence                   Last Occurrence           Downtime
172.29.10.12    31-JUL-10 08:12:50             01-AUG-10 09:00:00      1
172.29.11.54    01-AUG-10 11:12:00            01-AUG-10 01:10:00      3
172.29.58.7      07-AUG-10 04:10:00            07-AUG-10 05:00:00      2I will not have problem when I run the report on saturday as I can give condition as sysdate - 7.
First problem is how will I default to 8 AM.
Second if the report is run on sunday or in between before next saturdya I have to query the records only from satuday 8 AM to previous saturday 8 AM.
Can anyone please help me on this?
Thanks.
Ravi.

Answer 1

Hi,
hoek wrote:
That's a great hint, Solomon, thanks.
I always end up getting frustrated because trunc on a date returns a NULL for 'midnight'....and the ability to perform date arithmetic is gone all of a sudden. Why isn't Oracle just resetting to '00:00:00' when truncating a date, I wonder?I must not understand what you're asking.
It sounds as if you're saying that TRUNC (dt) sometimes returns something that is NULL (or somehow partially NULL), but I'm sure you don't really think that.
For other readers who may be wondering:
TRUNC (dt), where dt is a DATE (and not NULL) , always returns a DATE, and DATEs always have a time. Either the whole DATE is NULL or none of it is; you can't have a year-month-day in a DATE column and not have a time, or have a NULL time.
TRUNC(dt, x) may return a DATE where the time is not midnight, but only if x is a format string like 'MI' that specifies an interval less than a day. When x indicates a longer interval (e,g, 'IW'), or when x is omitted, the time is always midnight. In any event, you can do date arithmetic on the results.
I'm sure you understand this, but your question makes it sound like you don't.
This should illustrate my point:
-- generating hours, starting 14 days ago:
with t as (
select trunc(sysdate-14)+ level/24-1 dt
from   dual
connect by level <= 24*14
-- querying generated data:
select dt
--,      trunc(dt,'iw') - 5/3  -- great workaround, but why can't we just work with 00:00:00 for the time component?
from   t;
-- generating hours, starting 14 days ago:
with t as (
select trunc(sysdate-14)+ level/24-1 dt
from   dual
connect by level <= 24*14
-- querying data between saturday and previous saturday
-- from the same resultset and 'it doesn't work'
select dt
from   t
where  dt between trunc(dt-7)+8/24 and trunc(sysdate)+8/24;
Is this a parody of a poorly written question?
Are you trying to make the point that no one should ever say "it doesn't work" without explaining exactly what doesn't work, and what the expected output is?
I get the same 336 rows when I run either of the queries above.
As you've often said, posters should always show exactly what results they want.