I apologize, Ivan, in a quick read, I apparently confused your method with an earlier method. Indeed the multiple-join-same-table method not only works, but is the one often found in core (e.g. Taxonomy.module). I have not benchmarked either one, but I am going to assume that some core developer has at some time and that whoever that was discovered that either it is faster or that it is the best cross-database implementation. I do, however, feel that the EXISTS method is a more elegant and straight-forward solution, at least in MySql.