---
title: union() function
description: union() merges two or more input streams into a single output stream.
url: https://docs.influxdata.com/flux/v0/stdlib/universe/union/
estimated_tokens: 3729
product: Flux
version: v0
---

# union() function

-   Flux 0.7.0+
-   View InfluxDB support

`union()` merges two or more input streams into a single output stream.

The output schemas of `union()` is the union of all input schemas. `union()` does not preserve the sort order of the rows within tables. Use `sort()` if you need a specific sort order.

### Union vs join

`union()` does not modify data in rows, but unions separate streams of tables into a single stream of tables and groups rows of data based on existing group keys. `join()` creates new rows based on common values in one or more specified columns. Output rows also contain the differing values from each of the joined streams.

##### Function type signature

```js
(tables: [stream[A]]) => stream[A] where A: Record
```

For more information, see [Function type signatures](/flux/v0/function-type-signatures/).

## Parameters

### tables

(Required) List of two or more streams of tables to union together.

## Examples

-   [Union two streams of tables with unique group keys](#union-two-streams-of-tables-with-unique-group-keys)
-   [Union two streams of tables with empty group keys](#union-two-streams-of-tables-with-empty-group-keys)

### Union two streams of tables with unique group keys

```js
import "generate"

t1 =
    generate.from(
        count: 4,
        fn: (n) => n + 1,
        start: 2022-01-01T00:00:00Z,
        stop: 2022-01-05T00:00:00Z,
    )
        |> set(key: "tag", value: "foo")
        |> group(columns: ["tag"])

t2 =
    generate.from(
        count: 4,
        fn: (n) => n * (-1),
        start: 2022-01-01T00:00:00Z,
        stop: 2022-01-05T00:00:00Z,
    )
        |> set(key: "tag", value: "bar")
        |> group(columns: ["tag"])

union(tables: [t1, t2])
```

[](#view-example-output)

View example output

#### Output data

| _time | _value | *tag |
| --- | --- | --- |
| 2022-01-01T00:00:00Z | 0 | bar |
| 2022-01-02T00:00:00Z | -1 | bar |
| 2022-01-03T00:00:00Z | -2 | bar |
| 2022-01-04T00:00:00Z | -3 | bar |

| _time | _value | *tag |
| --- | --- | --- |
| 2022-01-01T00:00:00Z | 1 | foo |
| 2022-01-02T00:00:00Z | 2 | foo |
| 2022-01-03T00:00:00Z | 3 | foo |
| 2022-01-04T00:00:00Z | 4 | foo |

### Union two streams of tables with empty group keys

```js
import "generate"

t1 =
    generate.from(
        count: 4,
        fn: (n) => n + 1,
        start: 2021-01-01T00:00:00Z,
        stop: 2021-01-05T00:00:00Z,
    )
        |> set(key: "tag", value: "foo")
        |> group()

t2 =
    generate.from(
        count: 4,
        fn: (n) => n * (-1),
        start: 2021-01-01T00:00:00Z,
        stop: 2021-01-05T00:00:00Z,
    )
        |> set(key: "tag", value: "bar")
        |> group()

union(tables: [t1, t2])
```

[](#view-example-output)

View example output

#### Output data

| _time | _value | tag |
| --- | --- | --- |
| 2021-01-01T00:00:00Z | 1 | foo |
| 2021-01-02T00:00:00Z | 2 | foo |
| 2021-01-03T00:00:00Z | 3 | foo |
| 2021-01-04T00:00:00Z | 4 | foo |
| 2021-01-01T00:00:00Z | 0 | bar |
| 2021-01-02T00:00:00Z | -1 | bar |
| 2021-01-03T00:00:00Z | -2 | bar |
| 2021-01-04T00:00:00Z | -3 | bar |

#### Related

-   [join() function](/flux/v0/stdlib/universe/join/)

[transformations](/flux/v0/tags/transformations/)