John,
Add a field to the SELECT that contains int(age/10)*10. This will give you the number of complete decades (if the person is 30-39 it'll show '30', etc.).

HTH
Barbara

>Hi,
> I have member.birthday field in my table. I get the formula to calculate members' age. How should I group them base on their age such as 10, 20, 30, and ...?
>
>Thank you