Re: Grouping by timestamp, how to return 0 when there's no record

On 19 September 2011 12:01, Koen Van Impe <koen(dot)vanimpe(at)belnet(dot)be> wrote:

> Hello,
>
> I'm trying to write a query that groups records by hour.
> This works fine but when there are no records for a specific hour the
> query does not return a result (this seems 'logic') and I'd like it to
> return '0'. I suspect I should play around with 'interval' or something
> but I can't get it to work.
>

If you're working with an interval of time that's known when issuing the
query, you can add the missing hours by joining your results with
generate_series().

If not, you'll probably have to create a table with enough dates and hours
to join against, for which generate_series() is once again quite
convenient. I'd like to see a resultset similar to this

It works like this:
select hours.h from generate_series(0, 23) AS hours(h);

Alban.
--
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Cut the trees and you'll see there is no forest.