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:
- Get started with Flux for a conceptual overview of Flux and parts of a Flux query.
- Execute queries to discover a variety of ways to run your queries.
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: "db/rp")
|> 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
human_readable: 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=<-) => 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,
}),
)
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