Re: Time Aggregates

> > SELECT symbol, date_trunc('minute', posted),
> > min(price), max(price), avg(price)
> > FROM trade
> > GROUP BY symbol, date_trunc('minute', posted);

Hmmm... I'm not sure how to go about doing this for, say, 5 minute
intervals. Basically, I want a function:

date_round( timestamp, timespan ) --> timestamp

that will round the timestamp to the "nearest" timespan interval,
counting back from, say, the current time.

date_round( '1/1/99 15:21', '5 minutes' ) --> '1/1/99 15:20'

if the current time is, say, 12:00. As I see it, this involves

1. calculating the interval between now and the timestamp;
2. rounding that interval to the nearest multiple of the supplied interval;
3. adding the rounded interval to the current time.

It's step 2 that I can't quite figure out. I'm thinking about using
date_part( 'epoch', ... ) and some arithmetic. Will that be OK? Has
anyone done this before?

-itai

PS. I'll also be happy if the function is called 'date_trunc' :)

PPS. I expect this query to be called much less often than inserts to
the table.