Why are the Preview results different from the Run results?

The Preview will show you the results of your Selection and will calculate the number of records in your results. This allows you to see if the results meet your expectations. If not, you can go back and edit your Selection and run a new preview.  However, this count might differ from the final count when you actually Run the Selection.

There are a couple of reasons on why this issue may occur:

• 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", DESelect 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.

How to resolve this?

Try running the 'Preview' again, this will update the data to the latest version, which may align with the 'Run' results.