如何在PostgreSQL中按时间间隔选择行？

Question

I have a table with timestamp field and usage field like this

            timestamp  | usage
'2015-06-13 13:45:58'  | 240
'2015-06-13 13:45:59'  | 480
'2015-06-13 13:46:00'  | 240
'2015-06-13 13:46:01'  | 320
 ...

I want to get sum of usage for a period of '1 week' with '30 minutes' interval. I can get data only for intervals in minute, hour, day and ...

SELECT date_trunc('minute', timestamp) as clock, sum(usage)
FROM my_table
WHERE timestamp > localtimestamp - INTERVAL '1 week'
GROUP BY clock

how to get data for intervals like '5 minutes', '30 minutes', '2 days' and ... .

Answer 1

Use the following to get what your after.

SELECT TIMESTAMP WITH TIME ZONE 'epoch' + INTERVAL '1 second' * round((extract('epoch' FROM timestamp) / 1800) * 1800) AS clock,  SUM(usage)
FROM my_table 
WHERE timestamp > localtimestamp - INTERVAL '1 week'
GROUP BY round(extract('epoch' FROM timestamp) / 1800)