how do I create a condition in oracledb?

Question

How do i create a condition on oracle db? I'm new on this db. I already create table called vehicle_parked, but i want to trigger vehicle number as NULL if parkedOnSite value is 'F' and the structure like this

vehicle_parked

 - parked_id number(4) PK
 - arrivalTime date
 - parkedOnSite varchar(1) // value will be T/F
 - vehicle_number varchar(8)

Thanks.

Answer 1

you can easily manipulate your data by creating a DML trigger that fires before your data is inserted into table, and changes data.

CREATE OR REPLACE TRIGGER trg_vehicle_parked
BEFORE INSERT OR UPDATE
   ON vehicle_parked
   FOR EACH ROW    
DECLARE

BEGIN
  if :new.parkedOnSite = 'F' then
   :new.vehicle_number := null;
  end if;
END;
/

In triggers, besides :new, we can use :old pseudo codes. They stand for the values of the columns before(:old) or after(:new) DML statements issued. Especially for an update or delete trigger you may compare your column's old and new values in a trigger as in the example :

if ( nvl(:old.vehicle_number,0) != nvl(:new.vehicle_number,0) ) then
  go_on_with_statement ....