Thanks for your replies. First of all I should say that it'll be a while before I need to implement this, I just wanted to check whether something already existed, and do a little research.

I did consider using SQL for this, but as sauoq has suggested, the statements will need to be edited by a completely non-technical user. graffs suggestion of storing the required sql statement is a neat one, but I think the end user would probably stumble over the syntax - ideally I'd like to make it as simple to read as possible. As far as the criteria go, the compound statements are probably a bad idea - once I get to actually structuring the syntax, I'll bear that in mind, thanks.

Finally, would this functionality be useful enough to others that it's worth bundling separately and uploading to CPAN if and when it gets implemented?

cheers.