Dovresti creare un trigger.
Prova questo
CREATE OR REPLACE TRIGGER my_trg
BEFORE INSERT OR UPDATE ON Relationships
FOR EACH ROW
declare
function i_Age(id int) return int is
li_res int;
begin
select p.Age
into li_res
from Persons p
where p.ID= id
and rownum=1;
return li_res;
exception when no_data_found then
return NULL; --or Throw Exception depend on your logic if some datas not found
end;
BEGIN
IF INSERTING OR UPDATING THEN
IF :NEW.Relation == 'child' and i_Age(:NEW.Person_ID) < i_Age(:NEW.Relative_ID) then
NULL; --Throw Exception or your logic
END IF;
END IF;
END;
