On Wed, 22 Sept 2021 at 21:05, Israel Brewster <ijbrewster@xxxxxxxxxx> wrote:
I was wondering if there was any way to improve the performance of this query:SELECT station,array_agg(distinct(channel)) as channels FROM data GROUP BY station;
If you have tables of possible stations and channels (and if not, why not?), then an EXISTS query, something like
SELECT stations.name, ARRAY_AGG(channels.name)
FROM stations, channels
WHERE EXISTS
(SELECT FROM data WHERE data.channels=channels.name AND data.station=stations.name)
GROUP BY stations.name
will usually be much faster, because it can stop scanning after the first match in the index.
FROM stations, channels
WHERE EXISTS
(SELECT FROM data WHERE data.channels=channels.name AND data.station=stations.name)
GROUP BY stations.name
will usually be much faster, because it can stop scanning after the first match in the index.
Geoff
