# delete

## Overview

The `delete` statement is used to delete one or more columns or rows from one or more DSETs.

## Syntax

**`delete columns [except]`***`ColName1 [... ColNameN]`*

**`delete blankcolumns`**

**`delete rows`**

**`delete dset`***`dset_id`*

## Details

### Deleting columns

The list of column names following the initial `delete columns` statement may be used in one of two ways:

1. The columns listed will be deleted
2. All columns *except* those listed will be deleted

Which method to use is determined by the presence (or otherwise) of the `except` keyword:

```
delete columns One Two Three         # Delete the listed columns
delete columns except One Two Three  # Delete all but the listed columns
```

{% hint style="warning" %}
When using the `except` keyword, all column names following it *must* belong to the same DSET
{% endhint %}

It is not possible to delete a column from a DSET which only contains a single column. When deleting a column, the memory used to index it, along with the memory used to store the contents of its cells is released. This may be useful in situations where memory is limited.

Deleting unwanted columns early in a Transcript task will also increase the the performance of many subsequent operations performed by the task.

The second keyword may be `column` instead of `columns`. Either way, the statement behaves identically.

### Deleting blank columns

The `delete blankcolumns` statement will delete columns that only contain blank values from the default DSET.

{% hint style="info" %}
It is not possible to completely empty a DSET using `delete blankcolumns`. In the event that the last remaining column in a DSET is blank then it will not be deleted.
{% endhint %}

### Deleting rows

In order to delete rows from a DSET a local filter must be in effect. A local filter is created using the [where](https://olddocs.exivity.io/3.4.3/data-pipelines/transform/language/where) statement.

When used within the body of a [where](https://olddocs.exivity.io/3.4.3/data-pipelines/transform/language/where) statement, `delete rows` will delete all rows in the DSET associated with the local filter where the condition is true. For more information on conditions, please refer to the [where](https://olddocs.exivity.io/3.4.3/data-pipelines/transform/language/where) article.

{% hint style="info" %}
Either `delete rows` or `delete row` may be used (both variations work in an identical manner)
{% endhint %}

## Deleting a DSET

The `delete dset` statement can be used to remove a DSET from memory. This may be useful in cases where a DSET is no longer required, for example after it has been used to enrich another DSET via the [correlate](https://olddocs.exivity.io/3.4.3/data-pipelines/transform/language/correlate) statement.

{% hint style="warning" %}
It is not possible to delete the default DSET.
{% endhint %}

## Examples

Delete the column *temp* from the default DSET and the column *Interim* from the *azure.Usage* DSET:\
`delete columns temp azure.Usage.Interim`

Delete any columns in the default DSET that have no values in any rows:\
`delete blankcolumns`

Delete all rows where the VMID is 1234

```
where ([VMID] == 1234) {
    delete rows
}
```

Delete the DSET *azure.rates*\
`delete dset azure.rates`