Recursive query syntax ambiguity

Hm, I had hoped that the DB2/ANSI syntax would only require making "WITH" a
fully reserved word, and not the other tokens it uses. Certainly for
non-recursive queries that's the case as the only other token it uses is "AS"
which is already a fully reserved word.

However to fully support the DB2/ANSI syntax we would definitely have an
ambiguity and I think we would have to make "CYCLE" a fully reserved word
which seems like a much bigger concession than "WITH". Observe the following
case:

WITH RECURSIVE foo (x,y) AS (select 1,2) SEARCH DEPTH FIRST BY x CYCLE x,y SET ...

The parser can't search arbitrarily far checking for a SET to see if the CYCLE
is a keyword or a binary operator. Even if it could things like this would be
entirely ambiguous:

WITH RECURSIVE foo (x,y) AS (select 1,2) SEARCH DEPTH FIRST BY x CYCLE x, y CYCLE y SET ...

I'm nowhere near actually implementing this functionality yet so there's no
pressing need for action. In fact I think the search clause is actually an
ANSIism that isn't supported by DB2 itself yet either.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com