Updating two tables at once

Question

Dear all;
I have a table called using_table with the following field
using_id        life_length          Period
123                   2                   years
124                   1                   months
125                   3                   daysnow i would like a situation whenever the life_length is updated or changed to a new number for the using_table, for instance, the 2 can be changed to 200. If that is the case, this change should be reflected on another table called info_table which has a field column called expiring date. In this table, the expiring date is bascially the mfg date + life_length (period) for that particular id. For example if the mfg date is 01/01/2010 then the expiry date is 01/01/2010 + 2 years(gotten from using_table) = 01/01/2012. Another example is if the mfg date is 01/01/2011 for that id, then expiry date is 01/01/2011 + 1 month (gotten from using_table) = 02/01/2011
see details of the info_table below
info_id              using_id                 mfgdate(MM/dd/YYYY)                Expiry date(MM/DD/YYYY)
A1                       123                          01/01/2010                                    01/01/2012
A2                       124                          01/01/2011                                     02/01/2011Any help will greatly be appreciated. Thank you.

Answer 1

You will need 2 triggers for this. The code i am posting DOES NOT account for a multi-user environment. By this i mean if you have 2 users making concurrent modifications to this data YOU WILL get corrupted data. The only way to avoid that it to lock the tables before allowing access to them (the entire table). This means that only 1 session gets to make changes to this data at a time ... you can read about that here
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:474221407101
As an aside, since you say you are new to Oracle i will share more non-solicited advice with you.
using_id varchar2(50) not null,
info_id varchar2(100)primary key,Don't use character data types to store numeric data. It's bad for a number of reason (all of which you can also read about on AskTom).
Here's the code for the triggers and a simple test case for each.
create or replace trigger i_dont_like_doing_this
after update on using_table
for each row
begin
   update info_table i
      set i.expiry =
         case
            when :new.period = 'years'
            then
               add_months(i.mfgdate, :new.life_length * 12)
            when :new.period = 'months'
            then
               add_months(i.mfgdate, :new.life_length)
            when :new.period = 'days'
            then
               i.mfgdate + :new.life_length
         end
   where
      i.using_id = :new.using_id;
end;
create or replace trigger i_still_dont_like_this
before insert on info_table
for each row
begin
   select
      case
         when u.period = 'years'
         then
            add_months(:new.mfgdate, u.life_length * 12)
         when u.period = 'months'
         then
            add_months(:new.mfgdate, u.life_length)
         when u.period = 'days'
         then
            :new.mfgdate + u.life_length
      end
   into
      :new.expiry   
   from
      using_table u
   where
      u.using_id = :new.using_id;
end;
TUBBY_TUBBZ?insert into info_table values ('1', '125', sysdate, null);
1 row created.
TUBBY_TUBBZ?select * from info_table;
INFO_ID                                                             USING_ID                              MFGDATE           EXPIRY
1                                                                 125                              02-AUG-2010 08 45:51 05-AUG-2010 08 45:51
1 row selected.
TUBBY_TUBBZ?update using_table set life_length = 10 where using_id = '125';
1 row updated.
TUBBY_TUBBZ?select * from info_table;
INFO_ID                                                             USING_ID                              MFGDATE           EXPIRY
1                                                                 125                              02-AUG-2010 08 45:51 12-AUG-2010 08 45:51
1 row selected.
TUBBY_TUBBZ?You mentioned in another post that you will disallow modification of the EXPIRY date column by users. I don't know how you plan to enforce this, but unless you have a VERY good design methodology and lots of experience, i really don't see this happening. I'm not trying to berate you, but i remember back to when i was a beginner in Oracle (10 years ago) and that isn't something i would have been capable of.
10 years later and there's still an exorbitant amount i don't know :(