In SQL you join tables. If it's indexed it's fast. Can you do this using text files from the prompt? Example: I'd like to investigate the most popular RSS readers Debian offers. $apt-cache search rss | cut -d' ' -f1 > rss.txt $wget http://popcon.debian.org/main/by_vote.gz I'd like to "filter" by_vote.gz to just the package names in "rss.txt". In SQL this would be a join. I'd like it to be "fast". Do I have to do this in SQL?