On Wed, Oct 26, 2005 at 06:16:13PM +0300, Volkan YAZICI wrote:
> => SELECT
> -> (SELECT count(id) FROM sales
> -> WHERE id = 2
> -> AND date_trunc('hour', dt) = '2005-10-25 21:00:00'),
> -> (SELECT count(id) FROM sales
> -> WHERE id = 2
> -> AND date_trunc('hour', dt) = '2005-10-25 22:00:00');
> ?column? | ?column?
> ----------+----------
> 6 | 2
> (1 row)
>
> Isn't it possible to combine these two SELECTs as one.
If you can accept multiple rows instead of multiple columns then
one way would be to group by the hour:
SELECT date_trunc('hour', dt) AS hour, count(*)
FROM sales
WHERE id = 2 AND date_trunc('hour', dt) IN ('2005-10-25 21:00:00', '2005-10-25 22:00:00')
GROUP BY hour
ORDER BY hour; hour | count
---------------------+-------2005-10-25 21:00:00 | 62005-10-25 22:00:00 | 2
(2 rows)
Here's another possibility, but I find it a bit ugly:
SELECT sum(CASE date_trunc('hour', dt) WHEN '2005-10-25 21:00:00' THEN 1 ELSE 0 END) AS
count1, sum(CASE date_trunc('hour', dt) WHEN '2005-10-25 22:00:00' THEN 1 ELSE 0
END)AS count2
FROM sales
WHERE id = 2;count1 | count2
--------+-------- 6 | 2
(1 row)
If you're looking for the fastest method then use EXPLAIN ANALYZE
on each to see what works best on your data set.
--
Michael Fuhr
