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Exists

content/shared/influxdb-v2/query-data/flux/exists.md

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Use the exists operator to check if a row record contains a column or if a column's value is null.

js
(r) => exists r.column

If you're just getting started with Flux queries, check out the following:

Use exists with row functions ( filter(), map(), reduce()) to check if a row includes a column or if the value for that column is null.

Filter null values

js
from(bucket: "example-bucket")
    |> range(start: -5m)
    |> filter(fn: (r) => exists r._value)

Map values based on existence

js
from(bucket: "default")
    |> range(start: -30s)
    |> map(
        fn: (r) => ({r with
            human_readable: if exists r._value then
                "${r._field} is ${string(v: r._value)}."
            else
                "${r._field} has no value.",
        }),
    )

Ignore null values in a custom aggregate function

js
customSumProduct = (tables=<-) => tables
    |> reduce(
        identity: {sum: 0.0, product: 1.0},
        fn: (r, accumulator) => ({r with
            sum: if exists r._value then
                r._value + accumulator.sum
            else
                accumulator.sum,
            product: if exists r._value then
                r.value * accumulator.product
            else
                accumulator.product,
        }),
    )

Check if a statically defined record contains a key

When you use the record literal syntax to statically define a record, Flux knows the record type and what keys to expect.

  • If the key exists in the static record, exists returns true.
  • If the key exists in the static record, but has a null value, exists returns false.
  • If the key does not exist in the static record, because the record type is statically known, exists returns an error.
js
import "internal/debug"

p = {
    firstName: "John",
    lastName: "Doe",
    age: 42,
    height: debug.null(type: "int"),
}

exists p.firstName
// Returns true

exists p.height
// Returns false

exists p.hairColor
// Returns "error: record is missing label hairColor"