Tableau Prep is being used for more than just loading into Tableau Desktop or publishing to Tableau Server/Online. At this time the order of fields as we see in the Profile pane in Prep is not necessarily maintained across all outputs, for example here's a forum thread:
There are times that we really need that as users, here are a couple of use cases:
- Prep is outputting a CSV that will be used by a variety of users (Tableau Desktop and other tools). Having primary key columns as the left-most columns is extremely helpful for users to immediately understand the data. Related to that, even having field ordering for Hyper files is useful to help Tableau users understand the file in Desktop's data grid when they first connect to the file.
- Prep is outputting a CSV that will be used by a downstream tool and that tool is expecting the columns to have a specific order. When Prep arbitrarily re-orders the columns it breaks those experts and reduces the utility of Prep.
My goal would be that whatever ordering is used in the last step prior to the Output step is the one that is maintained for the output for CSV files and any other file types Prep might add where ordering is important.