Referencial integrity

Question

Hello
I can insert a record into parent table even there is no record in child table.
However,if the child row doesnt exist, I cannot update a parent table.
What is the reason for this and what to do to overcome?
idle> select * from p;
         X
         2
         7
        15
        19
        20
idle> select * from c;
         X
         2
         7
        19
        15
idle> update p set x=21 where x=15;
update p set x=21 where x=15
ERROR at line 1:
ORA-02292: integrity constraint (SYS.SYS_C004407) violated - child record found

Answer 1

The Child Record exists when you are updating the parent table p.
Tip:Always Name your constraints
Here is what you should do
SQL> alter table p drop primary key cascade ;
Table altered.
SQL> alter table p add constraint pk_p$x primary key (x) ;
Table altered.
SQL> alter table c add constraint fk_c$x foreign key (x) references p(x) deferrable;
Table altered.
SQL> alter session set constraint = deferred ;
Session altered.
SQL> update p set x=21 where x=15;
1 row updated.
SQL> update c set x=21 where x=15;
1 row updated.
SQL> select * from p ;
         X
         2
         7
        19
        20
        21
SQL> select * from c;
         X
         2
         7
        21
        19
SQL> alter session set constraint = immediate ;
Session altered.HTH
SS