Oracle Timestamp Conversion with Dates - sql

Question

Assuming this has a simple solution, but I can't find it.
I'm trying to do some logic on a DATE field in Oracle. My desire is to take a DATE field and subtract X hours from it.
For instance: SELECT A.MyDATE - 100 Hours from dual;
however, I need a result in a timestamp format 'YYYY-MM-DD hh:mm'.
I've tried CAST(A.MyDATE as TIMESTAMP) - NUMTODSINTERVAL(100/24,'day') however it didn't work.
I found out that the issue is that the MyDATE field when cast to a timestamp still contained some residual time elements. How can I reset these??
Thanks!

Answer 1

You can just do this with subtraction:
select a.MyDate - 100.0/24
To convert to varchar:
select to_char(a.MyDate - 100.0/24, 'YYYY-MM-DD')
And, if you want to get rid of that pesky time on the date:
select trunc(a.MyDate - 100.0/24) as JustTheDate

Answer 2

The formats and dates in my example can be changed to any other formats and dates:
SELECT To_Timestamp(To_Char(Sysdate - INTERVAL '100' HOUR, 'MM/DD/YYYY HH24:MI'), 'MM/DD/YYYY HH24:MI')
FROM dual
/
Output:
2/4/2013 10:18:00.000000000 AM
To remove time element add Trunc() to any of your dates...:
SELECT Trunc(To_Timestamp(To_Char(Sysdate - INTERVAL '100' HOUR, 'MM/DD/YYYY HH24:MI'), 'MM/DD/YYYY HH24:MI'))
FROM dual
/
Output: 2/4/2013
Conversion/Casting - when using other dates in place of sysdate then add formats as in my other examples:
SELECT CAST(SYSDATE AS TIMESTAMP) - INTERVAL '100' HOUR FROM dual
/
Output: 2/4/2013 10:26:35.000000000 AM
SELECT start_date tstamp_to_date, CAST(start_date AS timestamp) date_to_tstamp FROM
(
SELECT to_date(to_char(to_timestamp ('2013-02-07 10:07:47.000' , 'YYYY-MM-DD HH24:MI:SS.FF'),'DD-MON-YYYY HH24:MI:SS'), 'DD-MON-YYYY HH24:MI:SS') start_date
FROM dual
)
/
Output:
tstamp_to_date date_to_tstamp
-------------------------------------------------------
2/7/2013 10:07:47 AM 2/7/2013 10:07:47.000000 AM

Answer 3

In Oracle, a DATE always has a day and a time component. Depending on the tool you are using and your session's NLS_DATE_FORMAT, it is entirely possible that the tool may not display the time component when you look at the data. But that is simply a display question, it has no impact on the actual data.
If you want to subtract 100 hours from midnight on the day that MyDate represents
SELECT TRUNC(MyDate) - interval '100' hour
FROM dual
This will return a DATE. If you want to return a string in a particular format
SELECT TO_CHAR( TRUNC(MyDate) - interval '100' hour, 'YYYY-MM-DD hh:mi am' )
FROM dual
Note that I'm assuming that there was a typo in your question. I assume that you want to display the minutes after the hour (mi) rather than the month (mm).

Answer 4

I am trying to fetch the records which is older than 30 days (from Mod_date) and I am using the below query and it is returning all the data and I want only 30 days old data.
Sample :- Mod_date 03-NOV-12 12.00.00.000000000 AM
Query :-
select Mod_date from fil_cnfact where Mod_date <= sysdate -30 order by Mod_date asc ;