I encountered a couple of problems when using subselects with unions. in fact, it bugged me so much, i switched back to 4.0.14 and went with tmp tables instead. just my experience. i believe 4.1.1 sorts out many of the basic problems encountered so far with subselects etc. however, not sure when it will be released. imho, if what you are doing is mission critical, don't go with 4.1 just yet.