declare 
  column_exists exception;
  pragma exception_init (column_exists , -01430);
begin 
  execute immediate 'ALTER TABLE EXCEPCION_PEAJE_VIGENCIA ADD (CASETAPEAJE_ID NUMBER(7))';
  exception when column_exists then null;
end;
/
declare 
  column_exists exception;
  except_02275  exception;

  pragma exception_init (column_exists , -01430);
  pragma exception_init (column_exists , -02275);
begin 
  execute immediate 'ALTER TABLE EXCEPCION_PEAJE_VIGENCIA ADD CONSTRAINT EXCPEAJEVIGENCIA_CASETA_FK FOREIGN KEY (CASETAPEAJE_ID) REFERENCES CASETA_PEAJE (CASETAPEAJE_ID)';
  
  exception 
    when column_exists then null;
    when except_02275 then null;
end;