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,
decode(ast.extension,
'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.