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.

p = {firstName: "John", lastName: "Doe", age: 42}

exists p.firstName
// Returns true

exists p.height
// 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

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

Map values based on existence

from(bucket: "default")
  |> range(start: -30s)
  |> map(fn: (r) => ({
      r with
        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

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

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