join.full() function

join.full() performs a full outer join on two table streams.

The function calls join.tables() with the method parameter set to "full".

Function type signature

(<-left: stream[A], as: (l: A, r: B) => C, on: (l: A, r: B) => bool, right: stream[B]) => stream[C] where A: Record, B: Record, C: Record

Parameters

left

Left input stream. Default is piped-forward data (<-).

right

(Required) Right input stream.

on

(Required) Function that takes a left and right record (l, and r respectively), and returns a boolean.

The body of the function must be a single boolean expression, consisting of one or more equality comparisons between a property of l and a property of r, each chained together by the and operator.

as

(Required) Function that takes a left and a right record (l and r respectively), and returns a record. The returned record is included in the final output.

Examples

Perform a full outer join

In a full outer join, either l or r could be a default record, but they will never both be a default record at the same time.

To get non-null values for the output record, check both l and r to see which contains the desired values.

The example below defines a function for the as parameter that appropriately handles the uncertainty of a full outer join.

v_left and v_right still use values from l and r directly, because we expect them to sometimes be null in the output table.

For more information about the behavior of outer joins, see the Outer joins section in the join package documentation.

import "array"
import "join"

left =
    array.from(
        rows: [
            {_time: 2022-01-01T00:00:00Z, _value: 1, label: "a"},
            {_time: 2022-01-01T00:00:00Z, _value: 2, label: "b"},
            {_time: 2022-01-01T00:00:00Z, _value: 3, label: "d"},
        ],
    )
right =
    array.from(
        rows: [
            {_time: 2022-01-01T00:00:00Z, _value: 0.4, id: "a"},
            {_time: 2022-01-01T00:00:00Z, _value: 0.5, id: "c"},
            {_time: 2022-01-01T00:00:00Z, _value: 0.6, id: "d"},
        ],
    )

join.full(
    left: left,
    right: right,
    on: (l, r) => l.label == r.id and l._time == r._time,
    as: (l, r) => {
        time = if exists l._time then l._time else r._time
        label = if exists l.label then l.label else r.id

        return {_time: time, label: label, v_left: l._value, v_right: r._value}
    },
)