Tom Lane wrote:
> SQL92 contains a construct "table1 UNION JOIN table2", which is defined
> essentially the same as "table1 FULL JOIN table2 ON false" --- you get
> all the rows of table1 null-extended into the table2 columns, and all
> the rows of table2 null-extended into the table1 columns, and no actual
> join rows.
>
> SQL99, however, deprecates this construct, and it's gone entirely in
> SQL2003. (They don't say *why* they got rid of it --- is it just
> because it's redundant, or was there some error in the definition?
> Date and Darwen obviously don't like it either, but don't say why.)
>
> We've got some vestigial support for this thing, but given the
> subsequent evolution of the standard it seems quite unlikely that
> we'll ever finish up the implementation. It'd make more sense to
> spend the work on allowing FULL JOIN ON FALSE, something that we
> don't accept today but I think wouldn't be much work to fix.
>
> So I'm proposing that we remove what's there. In particular we could
> get rid of the intermediate yylex() function in parser.c, which should
> save at least a few microseconds during every SQL command. I didn't
> have a problem with that function when it was put in, because I figured
> we'd find other cases where we needed extra lookahead, but so far we've
> not found any so I'm thinking we could save the overhead.
>
> Any objections?
Agreed.
-- Bruce Momjian http://candle.pha.pa.us SRA OSS, Inc. http://www.sraoss.com
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