Re: [HACKERS] Re: Join/table alias bug

Yes, this is what was eventually done... only emit warnings for tables
already in the RTE, as Tom mentioned.

> Peter Eisentraut <e99re41(at)DoCS(dot)UU(dot)SE> writes:
> > ... The reason this behaves that way is because queries
> > without from lists (SELECT my_tbl.a) are valid in PostgreSQL for
> > historical reasons, so we're stuck with it.
>
> Not only for historical reasons: there are cases where it allows you
> to do things you couldn't easily do otherwise. An example is deleting
> using a join:
>
> DELETE FROM target WHERE field1 = source.field2
>
> which deletes any record in target whose field1 matches any field2
> value in source. This isn't SQL92 since DELETE doesn't allow you
> to specify any tables except the target table in FROM. (Yeah,
> I know this example could be written with a subselect --- but with
> a more complex WHERE condition it gets harder to do that. Also
> slower.)
>
> > We've pondered many times about emitting warnings but a definite
> > consensus was never reached.
>
> Bruce had actually put in some code to emit warnings, but Thomas
> objected to it for reasons I don't recall clearly. I think it was
> an implementation issue rather than objecting to the idea of having
> warnings. AFAIR we had pretty much agreed that a warning would be
> a good idea.
>
> IIRC, Bruce's code would emit a warning whenever an implicit RTE was
> added. I think that might be overly verbose --- I'd be inclined to
> warn only in the case that an implicit RTE is added for a table that
> has an RTE already (under a different alias). That is the only
> situation I've seen user complaints about.
>
> regards, tom lane
>

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