On Thu, Dec 10, 2009 at 10:48 AM, Andrew Gierth <and...@tao11.riddles.org.uk> wrote: >>>>>> "Robert" == Robert Haas <robertmh...@gmail.com> writes: > > > On Thu, Dec 10, 2009 at 1:46 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> > >> My reading of the spec is that USING (and therefore NATURAL) is > >> defined to join identically named columns. Therefore, renaming > >> one of the input columns as the OP did *should* indeed *must* > >> break the view. The problem is not how to make it work, it's how > >> to give an error message that doesn't look like an internal > >> failure. > > Robert> That seems ugly and unnecessary. I think we might be able to > Robert> define ourselves out of this problem. We don't guarantee > Robert> (and have never guaranteed) that selecting from a stored view > Robert> will produce the same results as re-executing the original > Robert> query. For example, * refers the list of columns at > Robert> definition-time, not execution-time, and if a column is > Robert> renamed, the view still refers to the same column; it doesn't > Robert> start crashing, nor would we want it to. Similarly, here, > Robert> the USING is internally converted to an equality join on the > Robert> two columns, and the ambiguous output column is, I think, > Robert> resolved in favor of one of them. I think we can just say > Robert> that that conversion happens in toto at parse-time, just as > Robert> the *-to-column-list conversion and the > Robert> column-name-to-column-reference conversions do. This seems > Robert> like a significantly more useful behavior and as a fringe > Robert> benefit it simplifies the code. > > There's another possible solution (albeit a somewhat nontrivial one) > which came up when a bunch of us were talking about this one on IRC; > which is to handle the problem in the view deparse: if a column used > in a USING clause has been renamed, add an alias to the query that > renames it back, e.g. > select ... from table1 as table1(v,a) join ... using (v) > > This would have to affect all the other references to that same column > in the query, so you'd need to do something like this: before deparsing, > walk the query looking for offending USING clauses, and make a list of > renamings to apply to column names. > > I haven't tried actually implementing this, but I believe it is > possible.
What advantage does this offer? ...Robert -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs
