declare
  ja_existe  exception;
  pragma exception_init (ja_existe  , -00001);
begin
  execute immediate 'DELETE FROM CLASSE_INDICE_PEAJE';
  exception when ja_existe  then null;
end;
/
declare 
  column_exists exception;
  pragma exception_init (column_exists , -01430);
begin 
  execute immediate 'ALTER TABLE CLASSE_INDICE_PEAJE MODIFY (INDICE_PEAJE NUMERIC(7,2))';
  exception when column_exists then null;
end;