Oracle Query to Compare dates from Two Different tables

select 'LOG_1' AS LOG_SOURCE, TIME_CREATED,ENTRY_TEXT FROM LOG_1

UNION ALL

select 'LOG_2', TIME_CREATED,ENTRY_TEXT FROM LOG_2

ORDER BY 2

I formalize this kind of logic as a view so you can document and comment it.

CREATE OR REPLACE FORCE VIEW COMBINED_LOGS

(LOG_SOURCE,

TIME_CREATED,

ENTRY_TEXT ) AS

select 'LOG_1' , TIME_CREATED,ENTRY_TEXT FROM LOG_1

UNION ALL

select 'LOG_2', TIME_CREATED,ENTRY_TEXT FROM LOG_2;

COMMENT ON TABLE COMBINED_LOGS IS 'Explanatory comment goes here';

This works for me on Oracle 11g R2 and Oracle 9i, perhaps it was the use of keyword SOURCE as a column name which I have corrected to LOG_SOURCE

Edit: Corrected to UNION all after the comment. See here for more discussion on the details of UNIONS. This should be done for performance reasons and to ensure identical records are not removed.

I'll do it in stages to make it easier to understand.

I put your data into a table called EX_DATA - added a primary key as I assume you'll have one and it makes things a little easier:

create table ex_data
(
  contract_id number(18),
  expire_dt date,
  term_notice number(18),
  notice_freq varchar(20),
  notice_months number
);


insert into ex_data values(1,TO_DATE('01-MAR-2005','DD-MON-YYYY'), 60, 'YEARLY', 12);

insert into ex_data values(2,TO_DATE('01-DEC-2007','DD-MON-YYYY'), 30, 'MONTHLY', 1);

insert into ex_data values(3,TO_DATE('28-FEB-2008','DD-MON-YYYY') ,30, 'YEARLY', 12);

The next expiry date from the first given date will be:

select add_months(expire_dt, notice_months) as next_expiry
from ex_data;

Then, it follows that the notice period is a bit of easy date arithmetic too:

select add_months(expire_dt, notice_months) as next_expiry, 
       add_months(expire_dt, notice_months) - term_notice as notice_date
from ex_data;

Using DUAL as a source, generate expiry dates for lots of years:

select expire_dt as first_expiry_date,
       l as expiry_num,
       add_months(expire_dt,l*notice_months) as all_expiry_dates
from ( select level l from dual connect by level < 100 ) l, ex_data
order by l; 

The next expiration date, and the date they should have been contacted for renegotiation:

select first_expiry_date, all_expiry_dates as next_expiry_date, all_expiry_dates - term_notice as renegotiation_date
from
(
select expire_dt as first_expiry_date, l as expiry_period_num, term_notice, add_months(expire_dt, l*notice_months) as all_expiry_dates
from ( select level l from dual connect by level < 100 ) l, ex_data
)
where all_expiry_dates >sysdate
and all_expiry_dates - term_notice < sysdate 
;

But, that's not what I think you're asking. You want the next renewal date where the contact period hasn't yet been hit, which can be done as follows:

select * from (
select contract_id, first_expiry_date, all_expiry_dates as next_expiry_date, all_expiry_dates - term_notice as notification_date, ROW_NUMBER( ) OVER (PARTITION BY
contract_id ORDER BY all_expiry_dates) r
from
(
select contract_id, expire_dt as first_expiry_date, l as expiry_period_num, term_notice, add_months(expire_dt, l*notice_months) as all_expiry_dates, notice_months
from ( select level l from dual connect by level < 100 ) l, ex_data
)
where all_expiry_dates - term_notice > sysdate 
)
where r=1;

Can probably be done with some simple SYSDATE maths along with the source data, but my brain is a little slow this evening ;)