---
title: join package
description: >
  The `join` package provides functions that join two table streams together.
menu:
  flux_v0_ref:
    name: join 
    parent: stdlib
    identifier: join
weight: 11
cascade:
  flux/v0/tags: [transformations]
  introduced: 0.172.0
---

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The `join` package provides functions that join two table streams together.
Import the `join` package:

```js
import "join"
```

## Outer joins

The join transformation supports left, right, and full outer joins.

- **Left outer joins** generate at least one output row for each record in the left input stream.
  If a record in the left input stream does not have a match in the right input stream,
  `r` is substituted with a default record in the `as` function.
- **Right outer joins** generate at least one output row for each record in the right input stream.
  If a record in the right input stream does not have a match in the left input stream,
  `l` is substituted with a default record in the `as` function.
- **Full outer joins** generate at least one output row for each record in both input streams.
  If a record in either input stream doesn't have a match in the other input stream,
  one of the arguments to the `as` function is substituted with a default record
  (either `l` or `r`, depending on which one is missing the matching record)

A default record has the same columns as the records in the corresponding input
table, but only group key columns are populated with a value. All other columns
are null.

## Inner joins

Inner joins drop any records that don't have a match in the other input stream. There is no
need to account for default or unmatched records when performing an inner join.


## Functions

{{< children type="functions" show="pages" >}}