Output preview not available for Inner Join

@darshthakkar - as @ptaylor mentioned, when you are working with Pipeline Preview data and need to see data movement through the entire pipeline, you need to reduce your source data sets to a limited enough set that any snaps that can potentially filter data (i.e. Join, Filter, etc.) will still have data to pass. In your case, I would suggest putting a temporary filtering condition (i.e. Where Clause) on your database Select snap so that your data will match after the Join snap. Once you have verified that the pipeline logic is correct, simply remove the filter from your select and execute the entire pipeline and validate the complete results.