Re: GROUP BY hour

Nathan Thatcher escreveu:
> I have, what I imagine to be, a fairly simple question. I have a query
> that produces output for a line graph. Each row represents an interval
> on the graph.
>
> SELECT COUNT(call_id) AS value, EXTRACT(hour from start_time) AS hour
> FROM c_call WHERE start_time >= '2008-08-01 00:00:00' AND end_time <=
> '2008-08-01 23:59:59' GROUP BY hour
>
>
> This works great when there is data in each interval but when a given
> interval has no data the group is omitted. What is the best way to
> ensure that the result contains a row for each interval with the value
> field set to zero or null? The reporting tool is incapable of filling
> in the gaps.
>

Try:
SELECT s.hour::int, coalesce(t.value,0) FROM generate_series(0,23) AS
s(hour)
LEFT OUTER JOIN
(SELECT COUNT(call_id) AS value, EXTRACT(hour from start_time) AS hour
FROM c_call WHERE date_trunc('day',start_time) = '2008-08-01'
GROUP BY hour) AS t
ON s.hour = t.hour;

Osvaldo