Check if a value exists

This page documents an earlier version of InfluxDB. InfluxDB v2.7 is the latest stable version. View this page in the v2.7 documentation.

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

  1. (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

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

Map values based on existence

  1. from(bucket: "default")
  2.     |> range(start: -30s)
  3.     |> map(
  4.         fn: (r) => ({r with
  5.             human_readable: if exists r._value then
  6.                 "${r._field} is ${string(v: r._value)}."
  7.             else
  8.                 "${r._field} has no value.",
  9.         }),
  10.     )

Ignore null values in a custom aggregate function

  1. customSumProduct = (tables=<-) => tables
  2.     |> reduce(
  3.         identity: {sum: 0.0, product: 1.0},
  4.         fn: (r, accumulator) => ({r with
  5.             sum: if exists r._value then
  6.                 r._value + accumulator.sum
  7.             else
  8.                 accumulator.sum,
  9.             product: if exists r._value then
  10.                 r.value * accumulator.product
  11.             else
  12.                 accumulator.product,
  13.         }),
  14.     )

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 does not exist in the static record, because the record type is statically known, exists returns an error.
  1. import "internal/debug"
  3. p = {
  4.     firstName: "John",
  5.     lastName: "Doe",
  6.     age: 42,
  7. }
  9. exists p.firstName
  10. // Returns true
  12. exists p.height
  13. // Returns "error: record is missing label height"

exists