The same alias is sometimes used in multiple (non-conflicting) aliases

We generally try to assign unique aliases to tables in the SQL tree. However, in some cases we do reuse the same alias; this occurs in non-conflicting contexts, i.e. where there's no scope overlap between the two contexts. So there's no functional impact at the moment as far as we know (though there may be databases out there which could have a problem with this); it's still a good idea to keep aliases as unique as possible for readability, at the very least.