165 lines
4.3 KiB
Markdown
165 lines
4.3 KiB
Markdown
---
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title: union() function
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description: >
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`union()` merges two or more input streams into a single output stream.
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menu:
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flux_v0_ref:
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name: union
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parent: universe
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identifier: universe/union
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weight: 101
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flux/v0/tags: [transformations]
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introduced: 0.7.0
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---
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<!------------------------------------------------------------------------------
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IMPORTANT: This page was generated from comments in the Flux source code. Any
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edits made directly to this page will be overwritten the next time the
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documentation is generated.
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To make updates to this documentation, update the function comments above the
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function definition in the Flux source code:
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https://github.com/influxdata/flux/blob/master/stdlib/universe/universe.flux#L2747-L2747
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Contributing to Flux: https://github.com/influxdata/flux#contributing
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Fluxdoc syntax: https://github.com/influxdata/flux/blob/master/docs/fluxdoc.md
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------------------------------------------------------------------------------->
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`union()` merges two or more input streams into a single output stream.
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The output schemas of `union()` is the union of all input schemas.
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`union()` does not preserve the sort order of the rows within tables.
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Use `sort()` if you need a specific sort order.
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### Union vs join
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`union()` does not modify data in rows, but unions separate streams of tables
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into a single stream of tables and groups rows of data based on existing group keys.
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`join()` creates new rows based on common values in one or more specified columns.
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Output rows also contain the differing values from each of the joined streams.
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##### Function type signature
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```js
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(tables: [stream[A]]) => stream[A] where A: Record
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```
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{{% caption %}}
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For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
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{{% /caption %}}
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## Parameters
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### tables
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({{< req >}})
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List of two or more streams of tables to union together.
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## Examples
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- [Union two streams of tables with unique group keys](#union-two-streams-of-tables-with-unique-group-keys)
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- [Union two streams of tables with empty group keys](#union-two-streams-of-tables-with-empty-group-keys)
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### Union two streams of tables with unique group keys
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```js
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import "generate"
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t1 =
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generate.from(
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count: 4,
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fn: (n) => n + 1,
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start: 2022-01-01T00:00:00Z,
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stop: 2022-01-05T00:00:00Z,
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)
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|> set(key: "tag", value: "foo")
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|> group(columns: ["tag"])
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t2 =
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generate.from(
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count: 4,
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fn: (n) => n * (-1),
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start: 2022-01-01T00:00:00Z,
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stop: 2022-01-05T00:00:00Z,
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)
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|> set(key: "tag", value: "bar")
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|> group(columns: ["tag"])
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union(tables: [t1, t2])
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```
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{{< expand-wrapper >}}
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{{% expand "View example output" %}}
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#### Output data
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2022-01-01T00:00:00Z | 0 | bar |
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| 2022-01-02T00:00:00Z | -1 | bar |
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| 2022-01-03T00:00:00Z | -2 | bar |
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| 2022-01-04T00:00:00Z | -3 | bar |
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| _time | _value | *tag |
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| -------------------- | ------- | ---- |
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| 2022-01-01T00:00:00Z | 1 | foo |
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| 2022-01-02T00:00:00Z | 2 | foo |
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| 2022-01-03T00:00:00Z | 3 | foo |
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| 2022-01-04T00:00:00Z | 4 | foo |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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### Union two streams of tables with empty group keys
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```js
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import "generate"
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t1 =
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generate.from(
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count: 4,
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fn: (n) => n + 1,
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start: 2021-01-01T00:00:00Z,
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stop: 2021-01-05T00:00:00Z,
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)
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|> set(key: "tag", value: "foo")
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|> group()
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t2 =
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generate.from(
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count: 4,
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fn: (n) => n * (-1),
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start: 2021-01-01T00:00:00Z,
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stop: 2021-01-05T00:00:00Z,
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)
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|> set(key: "tag", value: "bar")
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|> group()
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union(tables: [t1, t2])
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```
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{{< expand-wrapper >}}
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{{% expand "View example output" %}}
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#### Output data
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| _time | _value | tag |
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| -------------------- | ------- | ---- |
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| 2021-01-01T00:00:00Z | 1 | foo |
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| 2021-01-02T00:00:00Z | 2 | foo |
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| 2021-01-03T00:00:00Z | 3 | foo |
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| 2021-01-04T00:00:00Z | 4 | foo |
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| 2021-01-01T00:00:00Z | 0 | bar |
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| 2021-01-02T00:00:00Z | -1 | bar |
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| 2021-01-03T00:00:00Z | -2 | bar |
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| 2021-01-04T00:00:00Z | -3 | bar |
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{{% /expand %}}
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{{< /expand-wrapper >}}
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