Join two CSVs
Join two CSVs on a shared column. Inner keeps only matching rows, left/right keep every row from one side (blank cells for the other), outer keeps every row from both. A column name that collides with the other file gets a "_2" suffix. Runs entirely on your device.
Join two CSVs takes exactly two files and combines them on the column named in on. An inner join drops rows failing to match. Left and right keep one file's rows whole while blanking the other side's cells; outer keeps rows from either file. A duplicate column name in file two gets a _2 suffix, and a missing on column is refused.
Questions
What join types are supported?
Inner, left, right and outer, matched on the column named in on, which must exist in both files.
What if a column exists in both files besides the join column?
The second file's copy gets a _2 suffix added to its header name to avoid a collision.
How many files does it take?
Exactly 2; any other count is refused with the count given.
What if the on column does not exist?
It is refused, naming the file and listing that file's actual column names.
Does the summary line tell me anything useful?
Yes, it reports how many rows matched, how many were only in each file, and the total output row count.
What is the output file called?
joined.csv, one file no matter how many inputs you drop, with the key column written first.