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) not null,
  CONSTRAINT fk_supplier
    FOREIGN KEY (supplier_id)
    REFERENCES supplier (supplier_id)
);

INSERT INTO supplier
(supplier_id, supplier_name, contact_name)
VALUES (1000, 'Microsoft', 'Bill Gates');

INSERT INTO products
(product_id, supplier_id)
VALUES (50000, 1000);

DELETE from supplier
WHERE supplier_id = 1000;

ORA-02292: integrity constraint (IVANKA.FK_SUPPLIER) violated - child record found

create or replace trigger sup_t
before delete on supplier
for each row
declare
    e_no_delete exception;
pragma exception_init (e_no_delete,-02292);
begin
    dbms_output.put_line('awdw');
exception
      when  e_no_delete then
         dbms_output.put_line('Loooooooooooooooooooooooooooooooooo');
end;

ORA-02292: integrity constraint (IVANKA.FK_SUPPLIER) violated - child record found

create or replace trigger sup_t
after delete on supplier
for each row
begin 
        raise_application_error(-20001, 'My Text');
end;

delete from supplier where supplier_id=1

ORA-20001: My Text
ORA-06512: at "IVANKA.SUP_T", line 2
ORA-04088: error during execution of trigger 'IVANKA.SUP_T'

1. delete from supplier where supplier_id=1