An example given below for 

, when a value exists then 

 for that value to display the correspondent record else allow 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 empoyee id and if the employee id exists it will query the record else allow user to 

, the trigger written on key-next-item trigger, you can 

 the employees.fmb form also from the following link

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;