---
title: promql.join() function
description: >
  `promql.join()` joins two streams of tables on the **group key and `_time` column**.
  See [`experimental.join`](/flux/v0/stdlib/experimental/join/).
menu:
  flux_v0_ref:
    name: promql.join
    parent: internal/promql
    identifier: internal/promql/join
weight: 201
---

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`promql.join()` joins two streams of tables on the **group key and `_time` column**.
See [`experimental.join`](/flux/v0/stdlib/experimental/join/).

**Important**: The `internal/promql` package is not meant for external use.

##### Function type signature

```js
(fn: (left: A, right: B) => C, left: stream[A], 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
({{< req >}})
First of two streams of tables to join.



### right
({{< req >}})
Second of two streams of tables to join.



### fn
({{< req >}})
Function with left and right arguments that maps a new output record
using values from the `left` and `right` input records.
The return value must be a record.