PACKAGE primary_keygen IS
pkey varchar2(15);  
END;

CREATE OR REPLACE TRIGGER MASTER_NUM_GEN
BEFORE INSERT 
ON MASTER
FOR EACH ROW

DECLARE
 primary_key_value varchar2(15);
BEGIN
select lpad(to_char(ref_gen.nextval), 4,'0')
into primary_key_value from dual;
primary_keygen.pkey:='ABC/'||primary_key_value;
:new.Ref_Number:=primary_keygen.pkey;

END;

CREATE OR REPLACE TRIGGER DET1_NUM_GEN
BEFORE INSERT 
ON DETAIL1
FOR EACH ROW

BEGIN
if :new.M_ref_number is NULL THEN
:new.M_ref_number:=primary_keygen.pkey;
ENd if;
END;

CREATE OR REPLACE TRIGGER OREF_NUM_GEN
BEFORE INSERT
ON DETAIL2
FOR EACH ROW

BEGIN
if :new.O_ref_number is NULL THEN
:new.O_ref_number:=pkey_gen.master_key;
ENd if;

END;