If Both tables having References then how to insert the data each other

Question

Hai EveryOne..,
My Sample data.,
Create table emp (empno number primary key,ename varchar2(20));
Create table emp_dup (empno number references emp(empno),ename varchar2(20) primary key);
alter table emp add constraint ename_fk foreign key(ename) references emp(ename);
My Question is How to insert the data into these two tables?
Its a *"Circular Reference"* Concept.
Please ...
Thank You!!

Answer 1

You need to set the DEFERRED clause of the constraint when you create your foreign key as DEFERRABLE by which you can move the constraint validation at transaction level.
In an interview point of view that could be a reasonable answer. But in real time this could be strongly questionable.
Here is an example
SQL> create table emp1 (empno number, ename varchar2(10))
  2  /
Table created.
SQL> create table emp2 (empno number, ename varchar2(10))
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Table created. Define Primary Key for two tables
SQL> alter table emp1 add constraint emp1_pk primary key (empno)
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Table altered.
SQL> alter table emp2 add constraint emp2_pk primary key (ename)
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Table altered. Add foreign key for two tables with DEFERRED clause set as DEFERRABLE
SQL> alter table emp1 add constraint emp1_fk foreign key (ename) references emp2(ename) initially deferred deferrable
  2  /
Table altered.
SQL> alter table emp2 add constraint emp2_fk foreign key (empno) references emp1(empno) initially deferred deferrable
  2  /
Table altered. Now here is the test case
SQL> insert into emp1 values (1, 'karthick')
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1 row created.
SQL> commit      
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commit
ERROR at line 1:
ORA-02091: transaction rolled back
ORA-02291: integrity constraint (ARBORU.EMP1_FK) violated - parent key not found So the validation is done at Transaction level. Now let insert the value into both tables.
SQL> insert into emp1 values (1, 'karthick')
  2  /
1 row created.
SQL> insert into emp2 values (1, 'karthick')
  2  /
1 row created.
SQL> commit
  2  /
Commit complete.