How to compare dates in a PL/SQL procedure? - oracle

Question

I'm a newbie in SQL programming.
I need to make a procedure that will compare dates. The only argument in the procedure is a date typed in by the user in a Java program. I need to check if that argument (date) is before a year ago. In other words, I need to compare it with SYSDATE minus a year. If that is the case, I have to "purge" all of the tables related to "schedules" (there are 2 of them).
So for example, say the user types 2013-04-13, my procedure has to compare it with SYSDATE - 1 year (in that case, it would be 2014-12-03). Since the value is less than today minus a year, the tables "MovieSchedule" and "ChannelSchedule" have to be purged. If the entered date was 2014-12-16, since it's now more than SYSDATE minus a year, the procedure has to send back an explicit error that I will be able to use in the Java program.
Now, as I said I'm completely new to procedure programming in PL/SQL, so here is what I could come up with by looking up tutorials on the internet:
CREATE OR REPLACE
PROCEDURE purge_schedule(purgeDate date) AS
DECLARE
currentDate := to_date(SYSDATE, 'YYYMMDD');
BEGIN
-- IF purgeDate < (currentDate - 1year)
-- delete content in "MovieSchedule" and "ChannelSchedule"
-- ELSE
-- return explicit error
END purge_schedule;
I don't even know if any of this is the right way to write a procedure like I want. And as you can see, my problem is how to implement my condition in the procedure, not the logic behind it. I blame my lack of practice with the language.
Please tell me if I have to be more specific of if you need more information in order to help me. Thank you for your help and have a nice day :)

Answer 1

Step 1, define year. Should be obvious, but is not. I have found month and year definitions vary in the wild. I've seen year defined as 52 weeks, which is never an actual year, and 365 days, which matches one year a little less than 3 of every 4 years, and occasionally 360 days! (30 days / month * 12 months)
sysdate - 365 gives a date 365 days ago.
ADD_MONTHS(sysdate, -12) will give the date 12 months ago. In the case that sysdate is February 29, the result will be February 28 of the prior year.
sysdate - interval '1' year is tempting, but interval year to month arithmetic throws errors when the "result" is a day that is not there.
select date '2012-02-28' - interval '1' year from dual;
02/28/2011
select date '2012-02-29' - interval '1' year from dual;
ORA-01839: date not valid for month specified

Answer 2

It should fill your needs:
IF purgeDate < SYSDATE -365 THEN
...
END IF;

Answer 3

I have illustrated a below working code which help you. Let me know if this helps.
--Compiling the stored proc
CREATE OR REPLACE PROCEDURE purge_schedule(
purgeDate IN DATE )
AS
currentDate DATE:=SYSDATE;
BEGIN
IF purgeDate < ADD_MONTHS(SYSDATE,-12) THEN
DELETE FROM EMP;
DELETE FROM EMP_V1;
dbms_output.put_line('Records purged successfully');
ELSE
RAISE_APPLICATION_ERROR(-20001,'Date provided is not in range deletion not invoked',TRUE);
END IF;
END purge_schedule;
-- Exceuting the proc
set serveroutput on;
exec purge_schedule(to_date('12/12/2013','MM/DD/YYYY'));
-- Output
Records purged successfully
--Executing for negative scenario
set serveroutput on;
exec purge_schedule(TO_DATE('12/12/2017','MM/DD/YYYY'));
--Explicit exception raise
exec purge_schedule(TO_DATE('12/12/2017','MM/DD/YYYY'));
Error report -
ORA-20001: Date provided is not in range deletion not invoked
ORA-06512: at "AVROY.PURGE_SCHEDULE", line 11
ORA-06512: at line 1