Re: Allow an alias to be attached directly to a JOIN ... USING

On 2019-12-31 00:07, Vik Fearing wrote:
> One thing I notice is that the joined columns are still accessible from
> their respective table names when they should not be per spec.  That
> might be one of those "silly restrictions" that we choose to ignore, but
> it should probably be noted somewhere, at the very least in a code
> comment if not in user documentation. (This is my reading of SQL:2016 SR
> 11.a.i)

Here is a rebased patch.

The above comment is valid.  One reason I didn't implement it is that it 
would create inconsistencies with existing behavior, which is already 
nonstandard.

For example,

create table a (id int, a1 int, a2 int);
create table b (id int, b2 int, b3 int);

makes

select a.id from a join b using (id);

invalid.  Adding an explicit alias for the common column names doesn't 
change that semantically, because an implicit alias also exists if an 
explicit one isn't specified.

I agree that some documentation would be in order if we decide to leave 
it like this.

Another reason was that it seemed "impossible" to implement it before 
Tom's recent refactoring of the parse namespace handling.  Now we also 
have parse namespace columns tracked separately from range table 
entries, so it appears that this would be possible.  If we want to do it.

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
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