--- 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: 5969 product: Flux version: v0 --- # Join on time 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 *`_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/)