Subject: Re: Use JOIN USING aliases in ruleutils.c

From: Tom Lane <[email-masked]>
Date: Wed, 23 Mar 2022 11:14:23 -0400

Peter Eisentraut <[email-masked]> writes:
> When reverse-compiling a query, ruleutils.c has some complicated code to 
> handle the join output columns of a JOIN USING join.  There used to be 
> no way to qualify those columns, and so if there was a naming conflict 
> anywhere in the query, those output columns had to be renamed to be 
> unique throughout the query.

> Since PostgreSQL 14, we have a new feature that allows adding an alias 
> to a JOIN USING clause.  This provides a better solution to this 
> problem.

I looked this over briefly, and came away fairly dissatisfied.

My big fear is that it will reduce portability of pg_dump output:
views that would have loaded successfully into pre-v14 servers
no longer will, and your chances of porting them to other RDBMSes
probably go down too.  Once v13 becomes EOL, that will be less of a
concern, but I think it's a valid objection for awhile yet.

Also, it doesn't seem like we're getting much in return for the
portability hazard.  AFAICS the patch actually makes a net addition
of code to ruleutils.c, which perhaps means that you've not worked
hard enough on removing no-longer-needed code.  Maybe there's an
argument that the new output is more readable, but these regression
test changes don't look like any huge step forward to me.

> I also just named the generated 
> aliases "ju" with numbers added, maybe there are other ideas for how to 
> generate these names.

For my taste, names like "join_N" would be better.

On the whole, I'd recommend putting this idea on the back burner
for three or four years more.

			regards, tom lane

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From: Peter Eisentraut <[email-masked]>
Date: Fri, 25 Mar 2022 16:09:20 +0100

> concern, but I think it's a valid objection for awhile yet.

That's a good point.  I'll withdraw the patch for now.