Selecting an average of records grouped by 5 minute periods

Question

I'm having a slight issue. I have a PostgreSQL table with such format

time (datetime)     | players (int) | servers (int)
---------------------------------------------------
2013-12-06 13:40:01 | 80            | 20
2013-12-06 13:41:13 | 78            | 21
etc.

I would like to group them by 5 minute periods and get an average of the group as a single value, so there will be 20% of the records, each containing an average of ~5 numbers, with time set to the first time value in the group. I have no idea how to do this in PgSQL. So the result would be:

2013-12-06 13:40:01 | avg of players on :40, :41, :42, :43, :44 | same with servers
2013-12-06 13:45:05 | avg of players on :45, :46, :47, :48, :49 | same with servers
2013-12-06 13:50:09 | avg of players on :50, :51, :52, :53, :54 | same with servers
2013-12-06 13:55:12 | avg of players on :55, :56, :57, :58, :59 | same with servers

Answer 1

SELECT grid.t5
     , min(t."time") AS min_time
--   , array_agg(extract(min FROM t."time")) AS 'players_on'  -- optional
     , avg(t.players) AS avg_players
     , avg(t.servers) AS avg_servers
FROM  (
   SELECT generate_series(min("time")
                        , max("time")
                        , interval '5 min') AS t5
   FROM   tbl
   ) grid
LEFT   JOIN tbl t ON t."time" >= grid.t5
                 AND t."time" <  grid.t5 + interval '5 min'
GROUP  BY grid.t5
ORDER  BY grid.t5;

The subquery grid produces one row for every 5 minutes from minimum to maximum "time" in your table.

LEFT JOIN back to the table slicing data in 5-min intervals. Include the lower bound, exclude the upper border.
To drop 5-min slots where nothing happened, use JOIN instead of LEFT JOIN.

To have your grid-times start at 0:00, 5:00 etc, round down the min("time") in generate_series().

Related:

• Group by data intervals

• PostgreSQL: running count of rows for a query 'by minute'

Aside: I wouldn't use "time" as identifier. It's a reserved word in standard SQL and a function / type name in Postgres.

Answer 2

How about this?

select datepart('year', time) as StartYear, datepart('month', time) as StartMonth,
    datepart('day', time) as StartDay, datepart('hour', time) as StartHour,
    floor(datepart('minute', time)/5)*5 as StartMinute,
    avg(case when datepart('minute', time) = floor(datepart('minute', time)/5)*5 then players else null end) as Zero,
    avg(case when datepart('minute', time) = floor(datepart('minute', time)/5)*5+1 then players else null end) as One,
    avg(case when datepart('minute', time) = floor(datepart('minute', time)/5)*5+2 then players else null end) as Two,
    avg(case when datepart('minute', time) = floor(datepart('minute', time)/5)*5+3 then players else null end) as Three,
    avg(case when datepart('minute', time) = floor(datepart('minute', time)/5)*5+4 then players else null end) as Four,
from MyTable
group by datepart('year', time), datepart('month', time),
    datepart('day', time), datepart('hour', time),
    floor(datepart('minute', time)/5)*5

Answer 3

Try this, it should group minutes 0-4, 5-9, 10-14 and so on...

SELECT MIN(time), AVG(Players), AVG(Servers)
FROM MyTable t
GROUP BY date_trunc('hour', time),
    FLOOR(datepart('minute', time)/12)

EDIT: Changed the grouping to hour first and then to the Floor of minutes. I Think this should work.