An example is given below for Oracle Forms when a value exists then execute the query for that value to display the correspondent record else allow the user to create a new record for that value.
The following is the example given for HR schema employee table, in this example user will enter an employee id and if the employee id exists it will query the record else allow user to create a new record, the trigger written on key-next-item trigger, you can download the employees.fmb form also from the following link employees.fmb
KEY-NEXT-ITEM trigger code
declare
v_empid employees.employee_id%type;
Begin
Select employee_id into v_empid
from hr.employees
where employee_id = :employees.employee_id;
-- value exists
-- set block property and execute query
clear_block(no_validate);set_block_property('employees', default_where, 'employee_id = '||v_empid);
execute_query;
set_block_property('employees', default_where, '');
next_item;
exception
when no_data_found then
-- when not then clear block and allow to add new
v_empid := :employees.employee_id;
clear_block(no_validate);
:employees.employee_id := v_empid;
next_item;
End;