Hi,
Basically you would achieve this like this:
SELECT rightstr("0" || period, 2) AS DisplayPeriod FROM period_table
Depending on how you are considering using this (for some report's parameter?), you may also want to keep your period as a number:
SELECT rightstr("0" || period, 2) AS DisplayPeriod, period FROM period_table
If used as the source of a report's parameter and if your parameter's value need to be a numeric value, you could use both column as shown in the following screen shot:
Hope this helps,
Regards,