Perform an inner join

Use join.inner() to perform an inner join of two streams of data. Inner joins drop any rows from both input streams that do not have a matching row in the other stream.

Use join.inner to join your data

1. Import the join package.

2. Define the left and right data streams to join:

   • Each stream must have one or more columns with common values. Column labels do not need to match, but column values do.
   • Each stream should have identical group keys.

   For more information, see join data requirements.

3. Use join.inner() to join the two streams together. Provide the following required parameters:

   • left: Stream of data representing the left side of the join.
   • right: Stream of data representing the right side of the join.
   • on: Join predicate. For example: (l, r) => l.column == r.column.
   • as: Join output function that returns a record with values from each input stream. For example: (l, r) => ({l with column1: r.column1, column2: r.column2}).

The following example uses a filtered selection from the machineProduction sample data set as the left data stream and an ad-hoc table created with array.from() as the right data stream.

import "array"
import "influxdata/influxdb/sample"
import "join"

left =
    sample.data(set: "machineProduction")
        |> filter(fn: (r) => r.stationID == "g1" or r.stationID == "g2" or r.stationID == "g3")
        |> filter(fn: (r) => r._field == "oil_temp")
        |> limit(n: 5)

right =
    array.from(
        rows: [
            {station: "g1", opType: "auto", last_maintained: 2021-07-15T00:00:00Z},
            {station: "g2", opType: "manned", last_maintained: 2021-07-02T00:00:00Z},
        ],
    )

join.inner(
    left: left |> group(),
    right: right,
    on: (l, r) => l.stationID == r.station,
    as: (l, r) => ({l with opType: r.opType, maintained: r.last_maintained}),
)
    |> group(columns: ["stationID"])