declare
    column_exists exception;
    pragma exception_init (column_exists , -01430);
begin
    execute immediate 'ALTER TABLE TARIFA MODIFY (PRECIOORIGINAL NUMBER(10, 2))';
    execute immediate 'ALTER TABLE TARIFA_OFICIAL MODIFY (PRECIOORIGINAL NUMBER(10, 2), PRECIO NUMBER(10, 2))';
    execute immediate 'ALTER TABLE TARIFA_HIST MODIFY (PRECIOORIGINAL NUMBER(10, 2), PRECIO NUMBER(10, 2))';
    exception when column_exists then null;
end;