How to Avoid Duplicate Employee Number in Custom Form

Question

Developing A new employee screen, where all the Personal, Assignment, Visa, Passort & Tickets are capture and send for approval. Once it is done. Scheduled Concurrent Program will pick the APPROVED records and create the Employee & Assignment in the HRMS.
In custom form the employee Number is Last Employee Number in HRMS and Get the Last Employee Number in Custom table (always Custom table employee is higher) and increment by 1 whichever is higher.
This code written on ON-INSERT trigger.
SELECT     MAX (TO_NUMBER(employee_number)) + 1 INTO v_max_empno
FROM     per_all_people_f
WHERE     employee_number != 99999
AND     REPLACE ( TRANSLATE (employee_number, '1234567890', '~~~~~~~~~~'),'~', NULL) IS NULL
AND     business_group_id = :parameter.bg_id ;
SELECT     MAX (TO_NUMBER(employee_num)) + 1 INTO v_max_empno2
FROM     xx_employee_details
WHERE     business_group_id = :parameter.bg_id ;
IF v_max_empno2 IS NOT NULL THEN
     v_emp_number := v_max_empno2 ;
ELSE
     v_emp_number := v_max_empno ;
END IF ;
:xxempdet.employee_num := v_emp_number ;
Issue.
The above is working fine only when data entered from single machine. When multple users are access this form we are getting Duplicate Employee Numbers.
I need to impliment the process which is Sales Order Number generation without GAPLESS.
Regards/Prasanth

Answer 1

Make use of Sequence and use sequence.nextval for fetching the next value to ensure unique values.
Thanks
Shree