How to check the meatadata of a table?

Connect to the data source and open the data source page. The metadata grid — the toggle sits above the preview — lists every field with its data type, the table it came from, and its remote field name.

From there you can rename fields, change data types, hide columns you will not use, and reset any of those changes, all without touching a worksheet.

The Data pane in a worksheet shows the same fields organised by role, which is where you set default aggregations, geographic roles and default formatting.

Hiding unused fields in the metadata grid before building an extract is worth doing as a habit — it makes the extract smaller and the field list easier to work with.