Entering sequence no in column of table already having data in SQL

  alter table AMM_PROD_DRUG_LICENCE add pdl_seq_no NUMBER(19,0);

update AMM_PROD_DRUG_LICENCE set pdl_Seq_no=1;

CREATE SEQUENCE pdl_sequence_no_seq
  START WITH 1
  INCREMENT BY 1
  CACHE 50;

UPDATE AMM_PROD_DRUG_LICENCE
   SET pdl_seq_no = pdl_sequence_no_seq.nextval;