| From: | Denis Hirn <denis(dot)hirn(at)uni-tuebingen(dot)de> |
|---|---|
| To: | Peter Eisentraut <peter(dot)eisentraut(at)enterprisedb(dot)com> |
| Cc: | vignesh C <vignesh21(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Pantelis Theodosiou <ypercube(at)gmail(dot)com>, David Fetter <david(at)fetter(dot)org>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Zhihong Yu <zyu(at)yugabyte(dot)com> |
| Subject: | Re: [PATCH] Allow multiple recursive self-references |
| Date: | 2022-01-15 10:01:09 |
| Message-ID: | 060fc03a-e1c0-965e-526a-d407b92afd87@uni-tuebingen.de |
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| Lists: | pgsql-hackers |
> On 14. Jan 2022, at 13:21, Peter Eisentraut
<peter(dot)eisentraut(at)enterprisedb(dot)com> wrote:
>
> There is nothing in there that says that certain branches of the
UNION in a recursive query mean certain things. In fact, it doesn't even
require the query to contain a UNION at all. It just says to iterate on
evaluating the query until a fixed point is reached. I think this
supports my claim that the associativity and commutativity of a UNION in
a recursive query still apply.
>
> This is all very complicated, so I don't claim this to be
authoritative, but I just don't see anything in the spec that supports
what you are saying.
Please also have a look at SQL:2016, 7.16 <query expression> General
Rules 2) c),
which defines the evaluation semantics of recursive queries. I think
that this part
of the SQL standard refutes your argument.
Best,
-- Denis
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