---
title: join.inner() function
description: >
  `join.inner()` performs an inner join on two table streams.
menu:
  flux_v0_ref:
    name: join.inner
    parent: join
    identifier: join/inner
weight: 101
flux/v0/tags: [transformations]
introduced: 0.172.0
---

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`join.inner()` performs an inner join on two table streams.

The function calls `join.tables()` with the `method` parameter set to `"inner"`.

##### Function type signature

```js
(<-left: stream[A], as: (l: A, r: B) => C, on: (l: A, r: B) => bool, right: stream[B]) => stream[C] where A: Record, B: Record, C: Record
```

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

## Parameters

### left

Left input stream. Default is piped-forward data (<-).



### right
({{< req >}})
Right input stream.



### on
({{< req >}})
Function that takes a left and right record (`l`, and `r` respectively), and returns a boolean.

The body of the function must be a single boolean expression, consisting of one
or more equality comparisons between a property of `l` and a property of `r`,
each chained together by the `and` operator.

### as
({{< req >}})
Function that takes a left and a right record (`l` and `r` respectively), and returns a record.
The returned record is included in the final output.




## Examples

### Perform an inner join

```js
import "sampledata"
import "join"

ints = sampledata.int()
strings = sampledata.string()

join.inner(
    left: ints,
    right: strings,
    on: (l, r) => l._time == r._time,
    as: (l, r) => ({l with label: r._value}),
)

```

{{< expand-wrapper >}}
{{% expand "View example output" %}}

#### Output data

| _time                | _value  | label       | *tag |
| -------------------- | ------- | ----------- | ---- |
| 2021-01-01T00:00:00Z | -2      | smpl_g9qczs | t1   |
| 2021-01-01T00:00:10Z | 10      | smpl_0mgv9n | t1   |
| 2021-01-01T00:00:20Z | 7       | smpl_phw664 | t1   |
| 2021-01-01T00:00:30Z | 17      | smpl_guvzy4 | t1   |
| 2021-01-01T00:00:40Z | 15      | smpl_5v3cce | t1   |
| 2021-01-01T00:00:50Z | 4       | smpl_s9fmgy | t1   |

| _time                | _value  | label       | *tag |
| -------------------- | ------- | ----------- | ---- |
| 2021-01-01T00:00:00Z | 19      | smpl_b5eida | t2   |
| 2021-01-01T00:00:10Z | 4       | smpl_eu4oxp | t2   |
| 2021-01-01T00:00:20Z | -3      | smpl_5g7tz4 | t2   |
| 2021-01-01T00:00:30Z | 19      | smpl_sox1ut | t2   |
| 2021-01-01T00:00:40Z | 13      | smpl_wfm757 | t2   |
| 2021-01-01T00:00:50Z | 1       | smpl_dtn2bv | t2   |

{{% /expand %}}
{{< /expand-wrapper >}}