Oracle 21c

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create table empl (
  eid number(10,0) PRIMARY KEY not null 
, ename varchar2(50) not null
, dept_id number(10,0) not null
);



create table dept (
  did number(10,0) primary key not null 
, dname varchar2(50) not null
, manager_id number(10,0) not null
);
create table tmp (
  id number(10,0) primary key not null 
, name varchar2(50) not null
, reid number(10,0) not null
);
insert into tmp(id,name,reid) values(1,'A',1)
1 rows affected

ALTER TABLE dept
  ADD CONSTRAINT X1
    FOREIGN KEY (manager_id) REFERENCES empl (eid) 
    INITIALLY DEFERRED DEFERRABLE;
    
ALTER TABLE empl
  ADD CONSTRAINT X2
    FOREIGN KEY (dept_id) REFERENCES dept(did) 
    INITIALLY DEFERRED DEFERRABLE;
insert all
into empl(eid,ename,dept_id) values(id,name,reid)
into dept(did,dname,manager_id) values(id,name,reid)
select * from tmp 
2 rows affected

select * from empl


EID
ENAME
DEPT_ID


1
A
1


select * from dept


DID
DNAME
MANAGER_ID


1
A
1