first of all I'd like to say that Sequel seems very promising, thank  
you Sharon. I'm currently writing a threaded daemon and I can't  
figure out how to build this SQL String.

I have an array of category ids which I use to select import records:
db[:imports].filter :category_id => categories.map(:id)

Since a category has multiple imports I only want the latest Import  
before a Date X for each category. Is this even possible?

I think that you need a field in that table in which you have to put the
timestamp. Maybe this feature that you want is present in some advanced
RDBMS like Oracle/DB2 or maybe Postgresql.

Best regards,

Alin