In the Preview screen, you are able to preview your final selection before actually running it. Preview will show you the first 20 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.
In Preview you can check:
- if you matched the Data Extensions right
- if your Target Data Extension contains the right columns
- if the right filters were applied
- if the number of results is as expected
- if the query executes without errors
To conclude, the difference between running Preview and Run is that Preview is a safe place, a step we take for validating the data and the results are NOT written to your Target Data Extension yet. This only happens when you hit the Run button.
Also, users who do understand SQL sometimes may want to see the query that DESelect Segment built, to make sure DESelect Segment built the query they wanted. This is now possible in a very easy way.
When you preview a Selection, a link View SQL Query becomes available on the Preview screen. When clicking this link, a modal pops up showing the SQL query DESelect Segment built in a nicely formatted way, complete with indentation and colors for easy reading.