last()

The last aggregate allows you to get the value of one column as ordered by another. For example, last(temperature, time) will return the latest temperature value based on time within an aggregate group.

Required Arguments

Sample Usage

Get the temperature every 5 minutes for each device over the past day:

SELECT device_id, time_bucket('5 minutes', time) AS interval,
  last(temp, time)
FROM metrics
WHERE time > now () - INTERVAL '1 day'
GROUP BY device_id, interval
ORDER BY interval DESC;

warning

The last and first commands do not use indexes, and instead perform a sequential scan through their groups. They are primarily used for ordered selection within a GROUP BY aggregate, and not as an alternative to an ORDER BY time DESC LIMIT 1 clause to find the latest value (which will use indexes).