CREATE TABLE supplier
( supplier_id numeric(10) not null,
  supplier_name varchar2(50) not null,
  contact_name varchar2(50),
  CONSTRAINT supplier_pk PRIMARY KEY (supplier_id)
);

CREATE TABLE products
( product_id numeric(10) not null,
  supplier_id numeric(10),
  supplier_name varchar2(50),
  CONSTRAINT fk_supplier_comp
    FOREIGN KEY (supplier_id)
    REFERENCES supplier(supplier_id)
    ON DELETE SET NULL
);

insert into supplier values(10,'rajesh','m')

insert into supplier values(20,'rajesh','m')


insert into products values(100,10,'m')

insert into products values(200,20,'m')



select * from supplier


select * from products 

delete from supplier where SUPPLIER_ID=10

SQL> select * from products
  2  /

PRODUCT_ID SUPPLIER_ID SUPPLIER_NAME
---------- ----------- --------------------
       100             m
       200          20 m


update products
set SUPPLIER_ID=40
where PRODUCT_ID=100


"ORA-02291: integrity constraint (APPS.FK_SUPPLIER_COMP) violated - parent key not found"

SQL> select * from supplier
  2  /

SUPPLIER_ID SUPPLIER_NAME                                      CONTACT_NAME
----------- -------------------------------------------------- ---------------------
         20 siva                                               m

SQL> select * from products
  2  /

PRODUCT_ID SUPPLIER_ID SUPPLIER_NAME
---------- ----------- --------------------------------------------------
       100             m
       200          20 m

create table xxc_sample(t1 number primary key);

create table xxc_sample1(t2 number references xxc_sample(t1));

insert into xxc_sample
values(1);

insert into xxc_sample1
values(1);

update xxc_sample
set t1 = 2
where t1 = 1;

xxc_sample
*
ORA-02292: integrity constraint (APPS.SYS_C001107136) violated - child record found


create or replace trigger xxc_update
after update of t1 on xxc_sample
for each row
begin
   update xxc_sample1
   set t2 = :new.t1
   where t2 = :old.t1;
end;


update xxc_sample
set t1= 2
where t1=1;

               
select * from xxc_sample

output T1: 2 

create table xxc_sample1(t2 number references xxc_sample(t1));