Peter,
> Consider JOIN to be a black-box function, then you'd be writing something
> like
>
> SELECT a.c1, count(a.c2)
> FROM func(a, b) AS r (c1, c2, c3, c4, c5)
> WHERE b.c5 = x
> GROUP BY c1; -- <== refers to r.c1
>
> Clearly in this case you cannot claim that in general a.c1 == r.c1.
>
> If the func() is an inner join, then the claim is true, but if it's an
> outer join it's not. The scoping rules for inner and outer joins are the
> same, and that might be considered a good thing.
I see what you mean ... though I still hold that it's an implementation issue,
rather than a theory one. That is, a human can easily tell the differences
when differently qualified table names are exactly equivalent even if a
parser cannot.
But I can definitely see where trying to accomodate this would be doing a
*lot* of programming to support sloppy syntax in a rather limited number of
useful cases.
More on BUGS
--
Josh Berkus
Aglio Database Solutions
San Francisco