khi gia

join on command line

join -t’,’ -1 2 -2 1 -o “1.1 0 2.2” -a 1 f1 f2

This create a join of 2 CSV files f1 and f2, using column 2 as key for f1 and column 1 for f2, printing column 1 fo f1 and the key and column 2 of f2, and ensuring all lines of f1 are in output (left outer join).