That depends on your definition of "undefined". The result of such bare columns will be taken from a single row in the group satisfying the aggregate. How that particular single row is chosen if there are multiple to choose from appears "undefined" to an uneducated consumer. (Hence the reference to eternal September) This is the same as saying **any sufficiently advanced technology appears to be magic** to those who do not understand the technology. However there is most certainly a result and it most certainly is the result of the working of a deterministic algorithm which chooses the particular row, so it is far from "undefined". In fact, the result is in fact guaranteed.