Columns coming from different operators may have the same internal names ("_colNN"). There exists a query in the form select b.cb, a.ca from a JOIN b ON ... JOIN x ON ...; (distilled from a more complex query), which runs ok w/o vectorization. With vectorization, it will run ok for most ca, but for some ca it will fail (or can probably return incorrect results). That is because when building column-to-VRG-index map in VectorizationContext, internal column name for ca that the first map join operator adds to the mapping may be the same as internal name for cb that the 2nd one tries to add. 2nd VMJ doesn't add it (see code in ctor), and when it's time for it to output stuff, it retrieves wrong index from the map by name, and then wrong vector from VRG.