---
title: Preview & Run
slug: segment/preview-and-run
docTags: 
createdAt: 2026-01-16T18:27:21.701Z
---

Running a Selection means executing the Selection and writing the results to your Target Data Extension.

## How it works

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### [Run Preview](docId\:AFVLoJMPg9lrvaBMVJrtl)

Validate the results and calculate the record count without writing data to your Target Data Extension. Previewing helps you verify Data Extension joins, column mappings, applied filters, and ensures the underlying SQL query executes without errors.
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### Run the Selection

Running a Selection executes the final query and permanently writes the matching results to your Target Data Extension. Once you run the Selection, the temporary Data Extension used for the preview is automatically deleted.

If you are satisfied with the results of your preview:

1. Click the **Run** button on the Selection.
2. Now you will be redirected to the Home page, where you can see the status of your Selection change. It will move from an orange processing icon to a green checkmark when completed. If the query fails, a red warning icon appears which you can click to get the details of the error.
3. As soon as the Selection is queued, you'll see the Last Run column be updated with the current date-time.
4. Once the Selection is completed, you'll see the calculation of the amount record goes through the same stages. Once completed, in the **Records** column you'll see the number of records in your result. 
5. All the results of your Selections are now written to the Target Data Extension.
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### Monitoring and execution status

After initiating a run, you can track its progress on the **Home** page. If a run fails, the entire transaction is reverted and no results are written to the Target Data Extension.

For more information, see [Selection Status Icon Guide](docId\:lM4lGs0rlCJ2E52EafXHg).

:::hint{type="warning"}
You cannot stop the execution of a Selection once the final run is initiated, since Unaric Segment manages Query Activities through the SFMC API.
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## Selection fails

If a Selection fails to run, the whole transaction will be reverted and no results will be written to your Target Data Extension. Selections fails are notified by a red warning icon on the **Overview** page next to the selection name. Click on the red warning icon to see the details of the error*.*

:::hint{type="warning"}
If you executed a Selection it's not possible to stop the execution until the Selection provides a result. As Unaric Segment manages query activities through SFMC API, we are limited to its functionality, and currently, stopping the execution of Queries is not doable.

If you are having issues with a Selection execution or need further assistance, reach out to support at [support@deselect.com](mailto\:support@deselect.com).
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## Preview and Run results count differs

In some cases, your **Preview** and **Run** results count might differ. This can be due to:

- **Preview data is not updated:** Data may have been updated between generating the Preview and running the Selection. As a result, the preview count may not reflect the latest data, potentially causing a discrepancy between the Preview and Run data.
- **Verify the Data Action of your Selection:** In case your Selection's Data Action is set to *'Update' *or* "Append"*, Unaric Segment will keep adding more data in a Data Extension that already contains data. The Preview uses a temporary table that is completely empty and only getting new records, which explains why the count is different.

To solve this, run the **Preview** again. This will update the data to the latest version and align it with the **Run** results.