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(fn: (r) => ({
  4.       r with
  5.       human_readable:
  6.         if exists r._value then "${r._field} is ${string(v:r._value)}."
  7.         else "${r._field} has no value."
  8.   }))

Ignore null values in a custom aggregate function

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

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