Oracle 18c

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create table table2 ( id primary key, date_ )
as
select 1, to_date( '28/12/2019', 'DD/MM/YYYY' ) from dual union all
select 2, to_date( '30/12/2019', 'DD/MM/YYYY' ) from dual ;
2 rows affected

create table table1 (
  id number generated always as identity start with 5000 primary key
, table2id number references table2( id )
) ;
select * from table2 ;


ID
DATE_


1
28-DEC-19

2
30-DEC-19


select * from table1 ;
merge into table1 C using table2 P on ( C.table2id = P.id )
when not matched then
  insert ( C.table2id ) values ( P.id ) ;
2 rows affected

select * from table1 ;


ID
TABLE2ID


5000
1

5001
2


create sequence t2seq start with 2000 increment by 1 ;
create or replace procedure insert2 ( dt_ date )
is
begin
  insert into table2 ( id, date_ ) values ( t2seq.nextval, dt_ ) ;
  insert into table1 ( table2id ) values ( t2seq.currval ) ;
  commit ;
end ;
/
begin
  for i in 100 .. 104
  loop 
    insert2( sysdate + i ) ;
  end loop;
end ;
/
1 rows affected

select * from table2 ;


ID
DATE_


1
28-DEC-19

2
30-DEC-19

2000
11-JUN-23

2001
12-JUN-23

2002
13-JUN-23

2003
14-JUN-23

2004
15-JUN-23


select * from table1 ;


ID
TABLE2ID


5000
1

5001
2

5002
2000

5003
2001

5004
2002

5005
2003

5006
2004


merge into table1 C using table2 P on ( C.table2id = P.id )
when not matched then
  insert ( C.table2id ) values ( P.id ) ;

ID	DATE_
1	28-DEC-19
2	30-DEC-19
2000	11-JUN-23
2001	12-JUN-23
2002	13-JUN-23
2003	14-JUN-23
2004	15-JUN-23