docs-v2/content/shared/influxdb-v2/query-data/common-queries/compare-values.md

{{% note %}} This example uses NOAA water sample data. {{% /note %}}

This example compares the value from the latest point to an average value stored in another bucket. This is useful when using the average value to calculate a threshold check.

The following query:

• Uses range() to define a time range.
• Gets the last value in the means bucket and compares it to the last value in the noaa bucket using last().
• Uses join() to combine the results
• Uses map() to calculate the differences

means = from(bucket: "weekly_means")
    |> range(start: 2019-09-01T00:00:00Z)
    |> last()
    |> keep(columns: ["_value", "location"])

latest = from(bucket: "noaa")
    |> range(start: 2019-09-01T00:00:00Z)
    |> filter(fn: (r) => r._measurement == "average_temperature")
    |> last()
    |> keep(columns: ["_value", "location"])

join(tables: {mean: means, reading: latest}, on: ["location"])
    |> map(fn: (r) => ({r with deviation: r._value_reading - r._value_mean}))

Example results

location	_value_mean	_value_reading	deviation
coyote_creek	79.82710622710623	89	9.172893772893772
santa_monica	80.20451339915374	85	4.79548660084626