If you want to find employees that have hit their work anniversary, create a (scheduler) job that runs every day.
In this, search for employees who are a whole year from their start date. Here's one way do find these:
create table employees as
select * from hr.employees;
update employees
set hire_date = add_months ( trunc ( sysdate ), -12 )
where employee_id = 100;
update employees
set hire_date = add_months ( trunc ( sysdate ), -24 )
where employee_id = 101;
create or replace view employee_hire_length as
select employee_id, hire_date,
round (
months_between ( sysdate, hire_date ) / 12
) employment_years
from employees
where months_between ( sysdate, hire_date ) / 12 =
round (
months_between ( sysdate, hire_date ) / 12
) ;
select * from employee_hire_length;
EMPLOYEE_ID HIRE_DATE EMPLOYMENT_YEARS
100 22-JAN-2019 1
101 22-JAN-2018 2
For details on how to turn this into a job, read:
https://oracle-base.com/articles/10g/scheduler-10g