# Extend Operator

## Overview

Add new calculated fields with `extend`.

```kusto
| extend <dest>=<expression>[, ...]
```

## Examples

{% hint style="info" %}
Example data

```kusto
let aws_alb = datatable [
  {"type": "https", "p_event_time": "2023-09-16 05:59:04.058", "sentBytes": 167},
  {"type": "https", "p_event_time": "2023-09-16 05:45:34.863", "sentBytes": 329},
  {"type": "https", "p_event_time": "2023-09-16 05:36:09.017", "sentBytes": 167},
  {"type": "https", "p_event_time": "2023-09-16 05:27:39.177", "sentBytes": 468992}
];
```

{% endhint %}

### Add a new field

The query below adds the field `sentKB`, which is calculated by dividing the value of `sentBytes` by `1024`:

```kusto
aws_alb
| extend sentKB = sentBytes / 1024
```

| EVENT                                                                                                      |
| ---------------------------------------------------------------------------------------------------------- |
| `{ "p_event_time": "2023-09-16 05:59:04.058", "sentBytes": 167, "sentKB": 0.1630859375, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:45:34.863", "sentBytes": 329, "sentKB": 0.3212890625, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:36:09.017", "sentBytes": 167, "sentKB": 0.1630859375, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:27:39.177", "sentBytes": 468992, "sentKB": 458, "type": "https" }`       |

### Add multiple new fields

The query below adds multiple fields, separated by commas:

```kusto
aws_alb
| extend sentKB = sentBytes / 1024, sentMB = sentKB / 1024
```

| EVENT                                                                                                                                       |
| ------------------------------------------------------------------------------------------------------------------------------------------- |
| `{ "p_event_time": "2023-09-16 05:59:04.058", "sentBytes": 167, "sentKB": 0.1630859375, "sentMB": 0.0001592636108398438, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:45:34.863", "sentBytes": 329, "sentKB": 0.3212890625, "sentMB": 0.0003137588500976562, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:36:09.017", "sentBytes": 167, "sentKB": 0.1630859375, "sentMB": 0.0001592636108398438, "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:27:39.177", "sentBytes": 468992, "sentKB": 458, "sentMB": 0.447265625, "type": "https" }`                 |

### Reference added fields in subsequent expressions

Added fields can be referenced in subsequent query expressions, for example in a [`where`](https://docs.panther.com/pantherflow/operators/where) operator:

```kusto
aws_alb
| extend sentKB = sentBytes / 1024
| where sentKB > 2
```

| EVENT                                                                                                |
| ---------------------------------------------------------------------------------------------------- |
| `{ "p_event_time": "2023-09-16 05:27:39.177", "sentBytes": 468992, "sentKB": 458, "type": "https" }` |

### Remove a field

Fields can also be removed using `extend` by setting them to `null`:

```kusto
aws_alb
| extend sentBytes = null
```

| EVENT                                                            |
| ---------------------------------------------------------------- |
| `{ "p_event_time": "2023-09-16 05:59:04.058", "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:45:34.863", "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:36:09.017", "type": "https" }` |
| `{ "p_event_time": "2023-09-16 05:27:39.177", "type": "https" }` |


---

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