You'd like a nice way to order the output of (Oracle) SQL in an arbitrary way? For instance, if you query a table with filenames and the customer first wants the files with extension xml, then pdf and finally raw, you could use a query like done below:

      select ast.filename,
                    'pdf', 1,
                    'raw', 2,
                    0)                 sort_order
      from   assets                    ast
      order  by sort_order

The syntax for decode is a bit confusing. Basically, it's a bit like a Java switch statement. First, name the column whose value you want to substitute. Then, you get the original-new value pairs. The final parameter is for the case where none of the original values match.