Check if a value exists

(r) => exists r.column

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

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.",
        }),
    )

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,
        }),
    )

import "internal/debug"

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

exists p.firstName
// Returns true

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