TL;DR InfluxDB Tech Tips – July 7, 2016

Jimmy Guerrero — July 7, 2016

In this post we recap the week’s most interesting InfluxDB and TICK-stack related issues, workarounds, how-tos and Q&A from GitHub, IRC and the InfluxDB Google Group that you might have missed.

Understanding unexpected fill() behavior

Q: I’m using `fill(0)` in my query but it doesn’t return any results. Is this the expected behavior?

A: If none of your data fall within your query’s time range, your query will return no results – even if your query includes `fill()`. This is how `fill()` currently works but there is an open issue to change that behavior.

For example:

Write one data point:

> INSERT invisible person=7 1467842220000000000
> SELECT * FROM "invisible"
name: invisible
time                   person
2016-07-06T21:57:00Z   7

Use `fill(0)` and query a time range that includes the point:

> SELECT mean("person") FROM "invisible" WHERE time >= '2016-07-06T21:57:00Z' AND time <= '2016-07-06T21:59:00Z' GROUP BY time(1m) fill(0)
name: invisible
time                   mean
2016-07-06T21:57:00Z   7
2016-07-06T21:58:00Z   0
2016-07-06T21:59:00Z   0

Use `fill(0)` and query a time range that doesn’t include the point:

> SELECT mean("person") FROM "invisible" WHERE time >= '2016-07-06T21:58:00Z' AND time <= '2016-07-06T21:59:00Z' GROUP BY time(1m) fill(0)

Querying for the latest point in a measurement

Q: I’m trying to find the last point in my measurement. I’ve included the query that I use to do that, but I’m wondering – is there a better way to do this?

> SELECT "dance_id" FROM "ballroom" ORDER BY time DESC LIMIT 1
name: ballroom
time                   dance_id
2016-07-06T20:26:10Z   103

A: Yes! There’s an InfluxQL function (`LAST()`) that returns the last point in a measurement:

> SELECT last("dance_id") FROM "ballroom"
name: ballroom
time                   last
2016-07-06T20:26:10Z   103

InfluxDB Tech Tips Video

Check out the video below from the June 2016 InfluxDB Meetup for tips on series cardinality, `INTO` queries, and more.

For more InfluxDB tips, see our Frequently Asked Questions page and feel free to post your questions in the InfluxDB users group.

What’s next?