create or replace type t_persondate as object (
  person number
 ,dt date
);
/

create or replace type tdate as table of t_persondate;
/

create or replace function pm20(person in number,p in date) return tdate
deterministic
is
 dt tdate;
begin
 select t_persondate(person,trunc(p+(level-1)/24/60,'MI')) bulk collect into dt from dual connect by level<22;
 return dt;
end;
/

create table test_t (
  person number not null
 ,dt date not null
 ,rg tdate
)
 NESTED TABLE rg store as test_t_store
;

create trigger test_t 
before insert or update on test_t 
for each row
begin
 :new.rg:=pm20(:new.person,:new.dt);
end;
/

create unique index test_t_ux on test_t_store(person,dt);

insert into test_t (person,dt)
 values (1,sysdate);

insert into test_t (person,dt)
 values (1,sysdate+21/24/60); 

insert into test_t (person,dt)
 values (1,sysdate+20/24/60);  
 
insert into test_t (person,dt)
 values (2,sysdate+11/24/60);