Check if a value exists

Use the Flux exists operator to check if a record contains a key or if that key’s value is null.

  1. p = {firstName: "John", lastName: "Doe", age: 42}
  3. exists p.firstName
  4. // Returns true
  6. exists p.height
  7. // Returns false

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.     )