Peter Eisentraut <peter.eisentraut@2ndquadrant.com> writes:
> On 12/20/17 10:29, Tom Lane wrote:
>> Please say that's just an Oracle-ism and not SQL standard, because it's
>> formally ambiguous.
> The SQL standard syntax appears to be something like
> "tablename" [ AS OF SYSTEM TIME 'something' ] [ [ AS ] "alias" ]
> That's not going to be fun to parse.
Bleah. In principle we could look two tokens ahead so as to recognize
"AS OF SYSTEM", but base_yylex is already a horrid mess with one-token
lookahead; I don't much want to try to extend it to that.
Possibly the most workable compromise is to use lookahead to convert
"AS OF" to "AS_LA OF", and then we could either just break using OF
as an alias, or add an extra production that allows "AS_LA OF" to
be treated as "AS alias" if it's not followed by the appropriate
stuff.
It's a shame that the SQL committee appears to be so ignorant of
standard parsing technology.
regards, tom lane