From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Oliver Elphick" <olly(at)lfix(dot)co(dot)uk> |
Cc: | pgsql-hackers(at)postgreSQL(dot)org |
Subject: | Re: [HACKERS] UNION not allowed in sub-selects? |
Date: | 1999-11-28 22:43:57 |
Message-ID: | 9039.943829037@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
"Oliver Elphick" <olly(at)lfix(dot)co(dot)uk> writes:
> In 6.5.3, it seems that UNION is not allowed inside a sub-select:
> Is this a permanent feature, an oversight, or something already on the TODO
> list?
The latter, as a moment's investigation would have shown you:
* Support UNION/INTERSECT/EXCEPT in sub-selects
Changing the grammar to allow it would be the work of a moment,
but the rewriter and other stages need more work. I've been putting
it off until we do the much-discussed, little-implemented querytree
representation redesign. It might be possible to fix this within the
current representation, but Except_Intersect_Rewrite() is so
ugly/grotty/broken that I don't really want to touch it until I can
discard it and rewrite from the ground up...
regards, tom lane
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