Importing data — What an update does and doesn't touch

Updating merges the incoming row into the record that's already there. Only columns with a value are written, so a blank cell never wipes what you already had — handy when your export only carries the fields that changed. Columns you left as “＋ New field” are added to the table as part of the import. Untick a column to leave it out entirely. Relation, Lookup and Rollup fields can't be mapping targets. Lookups and rollups are calculated, and text dropped into a relation would sit there looking linked while pointing at nothing — so those fields aren't offered, and a column aimed at one is skipped rather than filled with something misleading.