SQL Update Query - set attribute value to that of another attribute

I'm trying to perform an update on a large number of records involving setting an attribute to the value contained in another attribute - something along the lines of (conceptually):

update xxxxxx set attribute1=attribute2 where attribute1 is null

Is this possible? Any advice would be greatly appreciated.

Thanks!

Current version only supports simple sql statements, no joins.
So you can't do it with sql.

The other option is the LDIF export and import.