Thanks Alvaro.  That's good to know.  Actually I was spacing on the need 
for this.  The date_trunc function with group by actually works for me.
select sum(amount), date_trunc('week', period_end) as dt from time_data 
group by dt;
Alvaro Herrera wrote:
> Omar Eljumaily wrote:
>   
>> Thanks Tom and Richard for the tip on date_trunc.  Is it possible in an 
>> sql select statement to create an iterator? 
>>     
>
> Yes, use the generate_series() function.
>
>