---
title: Join on time
description: Use join.time() to join two streams of data based on time values in the _time column. This type of join operation is common when joining two streams of time series data.
url: https://docs.influxdata.com/flux/v0/join-data/time/
estimated_tokens: 3243
product: Flux
version: v0
publisher: InfluxData
canonical: https://docs.influxdata.com/flux/v0/join-data/time/
date: '2025-02-27T17:50:16-06:00'
lastmod: '2025-02-27T17:50:16-06:00'
---

Use [`join.time()`](/flux/v0/stdlib/join/time/) to join two streams of data
based on time values in the `_time` column.
This type of join operation is common when joining two streams of[time series data](/influxdb/v2/reference/glossary/#time-series-data).

`join.time()` can use any of the available join methods.
Which method you use depends on your desired behavior:

* **inner** *(Default)*:
  Drop any rows from both input streams that do not have a matching
  row in the other stream.

* **left**:
  Output a row for each row in the **left** data stream with data matching
  from the **right** data stream. If there is no matching data in the **right**data stream, non-group-key columns with values from the **right** data stream
  are *null*.

* **right**:
  Output a row for each row in the **right** data stream with data matching
  from the **left** data stream. If there is no matching data in the **left**data stream, non-group-key columns with values from the **left** data stream
  are *null*.

* **full**:
  Output a row for all rows in both the **left** and **right** input streams
  and join rows that match based on their `_time` value.

## Use join.time to join your data

1. Import the `join` package.

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

   * Each stream must also have a `_time` column.
   * 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](/flux/v0/get-started/data-model/#group-key).

   *For more information, see [join data requirements](/flux/v0/join-data/#data-requirements).*

3. Use `join.time()` to join the two streams together based on time values.
   Provide the following parameters:

   * `left`: (Required) Stream of data representing the left side of the join.
   * `right`: (Required) Stream of data representing the right side of the join.
   * `as`: (Required) [Join output function](/flux/v0/join-data/#join-output-function-as)that returns a record with values from each input stream.
     For example: `(l, r) => ({r with column1: l.column1, column2: l.column2})`.
   * `method`: Join method to use. Default is `inner`.

The following example uses a filtered selections from the[**machineProduction** sample data set](/flux/v0/stdlib/influxdata/influxdb/sample/data/#set)as the **left** and **right** data streams.

#### Example data grouping

The example below regroups both the left and right streams to remove the`_field` column from the group key.
Because `join.time()` only compares tables with matching[group key instances](/flux/v0/get-started/data-model/#example-group-key-instances),
to join streams with different `_field` column values, `_field` cannot be part
of the group key.

```js
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 == "pressure")
        |> limit(n: 5)
        |> group(columns: ["_time", "_value", "_field"], mode: "except")

right =
    sample.data(set: "machineProduction")
        |> filter(fn: (r) => r.stationID == "g1" or r.stationID == "g2" or r.stationID == "g3")
        |> filter(fn: (r) => r._field == "pressure_target")
        |> limit(n: 5)
        |> group(columns: ["_time", "_value", "_field"], mode: "except")

join.time(method: "left", left: left, right: right, as: (l, r) => ({l with target: r._value}))
```

[](#view-example-input-and-output-data)

View example input and output data

### Input

> [!Note]
> *`_start` and `_stop` columns have been omitted from input examples.*

#### left

|        \_time         |\_measurement|stationID|\_field |\_value |
|-----------------------|-------------|---------|--------|--------|
| 2021-08-01T00:00:00Z  |  machinery  |   g1    |pressure|110.2617|
|2021-08-01T00:00:11.51Z|  machinery  |   g1    |pressure|110.3506|
|2021-08-01T00:00:19.53Z|  machinery  |   g1    |pressure|110.1836|
|2021-08-01T00:00:25.1Z |  machinery  |   g1    |pressure|109.6387|
|2021-08-01T00:00:36.88Z|  machinery  |   g1    |pressure|110.5021|

|        \_time         |\_measurement|stationID|\_field |\_value |
|-----------------------|-------------|---------|--------|--------|
| 2021-08-01T00:00:00Z  |  machinery  |   g2    |pressure|105.392 |
|2021-08-01T00:00:27.93Z|  machinery  |   g2    |pressure|105.3786|
|2021-08-01T00:00:54.96Z|  machinery  |   g2    |pressure|105.4801|
|2021-08-01T00:01:17.27Z|  machinery  |   g2    |pressure|105.5656|
|2021-08-01T00:01:41.84Z|  machinery  |   g2    |pressure|105.5495|

|        \_time         |\_measurement|stationID|\_field |\_value |
|-----------------------|-------------|---------|--------|--------|
| 2021-08-01T00:00:00Z  |  machinery  |   g3    |pressure|110.5309|
|2021-08-01T00:00:14.46Z|  machinery  |   g3    |pressure|110.3746|
|2021-08-01T00:00:25.29Z|  machinery  |   g3    |pressure|110.3719|
|2021-08-01T00:00:38.77Z|  machinery  |   g3    |pressure|110.5362|
|2021-08-01T00:00:51.2Z |  machinery  |   g3    |pressure|110.4514|

#### right

|        \_time         |\_measurement|stationID|    \_field     |\_value|
|-----------------------|-------------|---------|----------------|-------|
| 2021-08-01T00:00:00Z  |  machinery  |   g1    |pressure\_target|  110  |
|2021-08-01T00:00:11.51Z|  machinery  |   g1    |pressure\_target|  110  |
|2021-08-01T00:00:19.53Z|  machinery  |   g1    |pressure\_target|  110  |
|2021-08-01T00:00:25.1Z |  machinery  |   g1    |pressure\_target|  110  |
|2021-08-01T00:00:36.88Z|  machinery  |   g1    |pressure\_target|  110  |

|        \_time         |\_measurement|stationID|    \_field     |\_value|
|-----------------------|-------------|---------|----------------|-------|
| 2021-08-01T00:00:00Z  |  machinery  |   g2    |pressure\_target|  105  |
|2021-08-01T00:00:27.93Z|  machinery  |   g2    |pressure\_target|  105  |
|2021-08-01T00:00:54.96Z|  machinery  |   g2    |pressure\_target|  105  |
|2021-08-01T00:01:17.27Z|  machinery  |   g2    |pressure\_target|  105  |
|2021-08-01T00:01:41.84Z|  machinery  |   g2    |pressure\_target|  105  |

|        \_time         |\_measurement|stationID|    \_field     |\_value|
|-----------------------|-------------|---------|----------------|-------|
| 2021-08-01T00:00:00Z  |  machinery  |   g3    |pressure\_target|  110  |
|2021-08-01T00:00:14.46Z|  machinery  |   g3    |pressure\_target|  110  |
|2021-08-01T00:00:25.29Z|  machinery  |   g3    |pressure\_target|  110  |
|2021-08-01T00:00:38.77Z|  machinery  |   g3    |pressure\_target|  110  |
|2021-08-01T00:00:51.2Z |  machinery  |   g3    |pressure\_target|  110  |

### Output

|        \_time         |\_measurement|stationID|\_field |\_value |target|
|-----------------------|-------------|---------|--------|--------|------|
| 2021-08-01T00:00:00Z  |  machinery  |   g1    |pressure|110.2617| 110  |
|2021-08-01T00:00:11.51Z|  machinery  |   g1    |pressure|110.3506| 110  |
|2021-08-01T00:00:19.53Z|  machinery  |   g1    |pressure|110.1836| 110  |
|2021-08-01T00:00:25.1Z |  machinery  |   g1    |pressure|109.6387| 110  |
|2021-08-01T00:00:36.88Z|  machinery  |   g1    |pressure|110.5021| 110  |

|        \_time         |\_measurement|stationID|\_field |\_value |target|
|-----------------------|-------------|---------|--------|--------|------|
| 2021-08-01T00:00:00Z  |  machinery  |   g2    |pressure|105.392 | 105  |
|2021-08-01T00:00:27.93Z|  machinery  |   g2    |pressure|105.3786| 105  |
|2021-08-01T00:00:54.96Z|  machinery  |   g2    |pressure|105.4801| 105  |
|2021-08-01T00:01:17.27Z|  machinery  |   g2    |pressure|105.5656| 105  |
|2021-08-01T00:01:41.84Z|  machinery  |   g2    |pressure|105.5495| 105  |

|        \_time         |\_measurement|stationID|\_field |\_value |target|
|-----------------------|-------------|---------|--------|--------|------|
| 2021-08-01T00:00:00Z  |  machinery  |   g3    |pressure|110.5309| 110  |
|2021-08-01T00:00:14.46Z|  machinery  |   g3    |pressure|110.3746| 110  |
|2021-08-01T00:00:25.29Z|  machinery  |   g3    |pressure|110.3719| 110  |
|2021-08-01T00:00:38.77Z|  machinery  |   g3    |pressure|110.5362| 110  |
|2021-08-01T00:00:51.2Z |  machinery  |   g3    |pressure|110.4514| 110  |

#### Related

* [Troubleshoot join operations](/flux/v0/join-data/troubleshoot-joins/)
* [join package](/flux/v0/stdlib/join/)
* [join.time() function](/flux/v0/stdlib/join/time/)
| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g1 | pressure | 110.2617 |
| 2021-08-01T00:00:11.51Z | machinery | g1 | pressure | 110.3506 |
| 2021-08-01T00:00:19.53Z | machinery | g1 | pressure | 110.1836 |
| 2021-08-01T00:00:25.1Z | machinery | g1 | pressure | 109.6387 |
| 2021-08-01T00:00:36.88Z | machinery | g1 | pressure | 110.5021 |

| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g2 | pressure | 105.392 |
| 2021-08-01T00:00:27.93Z | machinery | g2 | pressure | 105.3786 |
| 2021-08-01T00:00:54.96Z | machinery | g2 | pressure | 105.4801 |
| 2021-08-01T00:01:17.27Z | machinery | g2 | pressure | 105.5656 |
| 2021-08-01T00:01:41.84Z | machinery | g2 | pressure | 105.5495 |

| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g3 | pressure | 110.5309 |
| 2021-08-01T00:00:14.46Z | machinery | g3 | pressure | 110.3746 |
| 2021-08-01T00:00:25.29Z | machinery | g3 | pressure | 110.3719 |
| 2021-08-01T00:00:38.77Z | machinery | g3 | pressure | 110.5362 |
| 2021-08-01T00:00:51.2Z | machinery | g3 | pressure | 110.4514 |

| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g1 | pressure_target | 110 |
| 2021-08-01T00:00:11.51Z | machinery | g1 | pressure_target | 110 |
| 2021-08-01T00:00:19.53Z | machinery | g1 | pressure_target | 110 |
| 2021-08-01T00:00:25.1Z | machinery | g1 | pressure_target | 110 |
| 2021-08-01T00:00:36.88Z | machinery | g1 | pressure_target | 110 |

| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g2 | pressure_target | 105 |
| 2021-08-01T00:00:27.93Z | machinery | g2 | pressure_target | 105 |
| 2021-08-01T00:00:54.96Z | machinery | g2 | pressure_target | 105 |
| 2021-08-01T00:01:17.27Z | machinery | g2 | pressure_target | 105 |
| 2021-08-01T00:01:41.84Z | machinery | g2 | pressure_target | 105 |

| _time | _measurement | stationID | _field | _value |
| --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value |
| 2021-08-01T00:00:00Z | machinery | g3 | pressure_target | 110 |
| 2021-08-01T00:00:14.46Z | machinery | g3 | pressure_target | 110 |
| 2021-08-01T00:00:25.29Z | machinery | g3 | pressure_target | 110 |
| 2021-08-01T00:00:38.77Z | machinery | g3 | pressure_target | 110 |
| 2021-08-01T00:00:51.2Z | machinery | g3 | pressure_target | 110 |

| _time | _measurement | stationID | _field | _value | target |
| --- | --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value | target |
| 2021-08-01T00:00:00Z | machinery | g1 | pressure | 110.2617 | 110 |
| 2021-08-01T00:00:11.51Z | machinery | g1 | pressure | 110.3506 | 110 |
| 2021-08-01T00:00:19.53Z | machinery | g1 | pressure | 110.1836 | 110 |
| 2021-08-01T00:00:25.1Z | machinery | g1 | pressure | 109.6387 | 110 |
| 2021-08-01T00:00:36.88Z | machinery | g1 | pressure | 110.5021 | 110 |

| _time | _measurement | stationID | _field | _value | target |
| --- | --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value | target |
| 2021-08-01T00:00:00Z | machinery | g2 | pressure | 105.392 | 105 |
| 2021-08-01T00:00:27.93Z | machinery | g2 | pressure | 105.3786 | 105 |
| 2021-08-01T00:00:54.96Z | machinery | g2 | pressure | 105.4801 | 105 |
| 2021-08-01T00:01:17.27Z | machinery | g2 | pressure | 105.5656 | 105 |
| 2021-08-01T00:01:41.84Z | machinery | g2 | pressure | 105.5495 | 105 |

| _time | _measurement | stationID | _field | _value | target |
| --- | --- | --- | --- | --- | --- |
| _time | _measurement | stationID | _field | _value | target |
| 2021-08-01T00:00:00Z | machinery | g3 | pressure | 110.5309 | 110 |
| 2021-08-01T00:00:14.46Z | machinery | g3 | pressure | 110.3746 | 110 |
| 2021-08-01T00:00:25.29Z | machinery | g3 | pressure | 110.3719 | 110 |
| 2021-08-01T00:00:38.77Z | machinery | g3 | pressure | 110.5362 | 110 |
| 2021-08-01T00:00:51.2Z | machinery | g3 | pressure | 110.4514 | 110 |