at the bare minimum you can just select both columns, you actually don't get a performance hit. typical sql functions run faster, since they can deal with the raw data. I'm not sure how you'll see it between MySQL and php computing it
select other_columns, REPLACE(`article_title`,' ','-') article_title_dash, article_title FROM your_table;
and you would refer to the column article_title_dash.
Don't misjudge SQL by any means - you can write an entire application with just sql statements, using a server side language to display the output and parse passed parameters. Oracle's PL/SQL can actually take the place of a server side language - it's a derivative of Perl that can interact with a database directly.