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 amount of the 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
Note: when you run a preview, the results are NOT written to your target data extension yet. This only happens when you hit the Run button.