Join two tables with unique keys
A safe join begins with keys that identify one row on each side.
Check key uniqueness before matching
Repeated nonblank keys stop the join. This avoids silently multiplying rows in a many-to-many match. Blank keys never match one another and remain unmatched in left or full output.
Choose which unmatched records matter
Inner output keeps matched keys only. Left output keeps every first-table row and matching second-table fields. Full output also adds unmatched second-table rows. Pick the mode that fits the question rather than treating one as universally correct.
Inspect the result schema
The first key column represents both keys in the output. Other fields from the second table are appended, and name collisions receive a “(second)” suffix. Check those suffixed fields and unmatched blanks before exporting.
Try this workflow: Join tables by key. It loads a labelled fictional example that you can edit.