time_bucket()

time_bucket()

The time_bucket function is similar to the standard PostgreSQL date_trunc function. Unlike date_trunc, it allows for arbitrary time intervals instead of second, minute, and hour intervals. The return value is the bucket’s start time.

Note that daylight savings time boundaries means that the amount of data aggregated into a bucket after such a cast can be irregular. For example, if the bucket_width is 2 hours, the number of UTC hours bucketed by local time on daylight savings time boundaries can be either three hours or one hour.

Required arguments for interval time inputs

Name	Type	Description
`bucket_width`	INTERVAL	A PostgreSQL time interval for how long each bucket is
`ts`	TIMESTAMP or TIMESTAMPTZ	The timestamp to bucket

If you use months as an interval for bucket_width, you cannot combine it with a non-month component. For example, 1 month and 3 months are both valid bucket widths, but 1 month 1 day and 3 months 2 weeks are not.

Optional arguments for interval time inputs

Name	Type	Description
`timezone`	TEXT	The timezone for calculating bucket start and end times. Can only be used with `TIMESTAMPTZ`. Defaults to UTC.
`offset`	INTERVAL	The time interval to offset all time buckets by. A positive value shifts bucket start and end times later. A negative value shifts bucket start and end times earlier. `offset` must be surrounded with double quotes when used as a named argument, because it is a reserved key word in PostgreSQL.
`origin`	TIMESTAMP	Buckets are aligned relative to this timestamp. Defaults to midnight on January 3, 2000, for buckets that don’t include a month or year interval, and to midnight on January 1, 2000, for month, year, and century buckets.

Required arguments for integer time inputs

Name	Type	Description
`bucket_width`	INTEGER	The bucket width
`ts`	INTEGER	The timestamp to bucket

Optional arguments for integer time inputs

Name	Type	Description
`offset`	INTEGER	The amount to offset all buckets by. A positive value shifts bucket start and end times later. A negative value shifts bucket start and end times earlier. `offset` must be surrounded with double quotes when used as a named argument, because it is a reserved key word in PostgreSQL.

Sample usage

Simple five minute averaging:


SELECT time_bucket('5 minutes', time) AS five_min, avg(cpu)
FROM metrics
GROUP BY five_min
ORDER BY five_min DESC LIMIT 10;

To report the middle of the bucket, instead of the left edge:


SELECT time_bucket('5 minutes', time) + '2.5 minutes'
  AS five_min, avg(cpu)
FROM metrics
GROUP BY five_min
ORDER BY five_min DESC LIMIT 10;

For rounding, move the alignment so that the middle of the bucket is at the five minute mark, and report the middle of the bucket:


SELECT time_bucket('5 minutes', time, '-2.5 minutes'::INTERVAL) + '2.5 minutes'
  AS five_min, avg(cpu)
FROM metrics
GROUP BY five_min
ORDER BY five_min DESC LIMIT 10;

In this example, add the explicit cast to ensure that PostgreSQL chooses the correct function.

To shift the alignment of the buckets you can use the origin parameter passed as a timestamp, timestamptz, or date type. This example shifts the start of the week to a Sunday, instead of the default of Monday:


SELECT time_bucket('1 week', timetz, TIMESTAMPTZ '2017-12-31')
  AS one_week, avg(cpu)
FROM metrics
GROUP BY one_week
WHERE time > TIMESTAMPTZ '2017-12-01'  AND time < TIMESTAMPTZ '2018-01-03'
ORDER BY one_week DESC LIMIT 10;

The value of the origin parameter in this example is 2017-12-31, a Sunday within the period being analyzed. However, the origin provided to the function can be before, during, or after the data being analyzed. All buckets are calculated relative to this origin. So, in this example, any Sunday could have been used. Note that because time < TIMESTAMPTZ '2018-01-03' is used in this example, the last bucket would have only 4 days of data. This cast to TIMESTAMP converts the time to local time according to the server’s timezone setting.


SELECT time_bucket(INTERVAL '2 hours', timetz::TIMESTAMP)
  AS five_min, avg(cpu)
FROM metrics
GROUP BY five_min
ORDER BY five_min DESC LIMIT 10;

Bucket temperature values to calculate the average monthly temperature. Set the timezone to ‘Europe/Berlin’ so bucket start and end times are aligned to midnight in Berlin.


SELECT time_bucket('1 month', ts, 'Europe/Berlin') AS month_bucket,
  avg(temperature) AS avg_temp
FROM weather
GROUP BY month_bucket
ORDER BY month_bucket DESC LIMIT 10;