Re: [PATCH] Allow multiple recursive self-references

[Peter Eisentraut]

On 11.01.22 12:33, Denis Hirn wrote:
I have been studying this a bit more.  I don't understand your argument here.
Why would this query have different semantics than, say
WITH RECURSIVE t(n) AS (
     VALUES (1)
       UNION ALL
     VALUES (2)
       UNION ALL
     SELECT n+1 FROM t WHERE n < 100
) SELECT * FROM t LIMIT 100;

The order of UNION branches shouldn't be semantically relevant.

WITH RECURSIVE (ab)uses the (typically associative and commutative) UNION [ALL] 
clause,
and fundamentally changes the semantics – associativity and commutativity no 
longer apply.
I think your confusion stems from this ambiguity.

The language in the SQL standard does not support this statement.  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.