Xikui,
"(" SelectExpression ")" is permitted by the Subquery() production, and
Subquery() itself is one of the alternatives in the ParenthesizedExpression().
What is the compilation issue you were trying to solve?
Thanks,
-- Dmitry
On 3/14/18, 11:52 PM, "Mike Carey" <[email protected]> wrote:
Not sure, but I don't think this is (nearly) sufficient context/info to
see what's going on. With the current factoring of things, any other
place that includes Expression is not going to allow a SelectExpression
to appear directly as an Expression. Your change would - which might be
a major change, syntactically, that might lead to a variety of
ambiguities. Without looking at the whole grammar one can't tell. I
would guess that if you look, you may find that you can have a
SelectExpression as a query if and only if its enclosed in parentheses,
which might be by design to avoid ambiguities. Have a look at that....
(Basically, look at the other uses of Expression in the grammar - and/or
look to see if "(" SelectExpression ")" is permitted if you follow
through the grammar from Expression.
On 3/14/18 8:59 PM, Xikui Wang wrote:
> Dear Devs,
>
> I'm trying to fix a compilation issue with the subquery in SQLPP and got a
> question about the specification of "Expression". Here is the current
> grammar of "Query" and "Expression" in SQLPP:
>
> Query::=( Expression | SelectExpression )
> Expression::=( OperatorExpr | CaseExpr | QuantifiedExpression )
>
> I'm wondering why "SelectExpression" is not in the specification of
> "Expression" but in "Query". When I looked back to the AQL specification,
I
> found that we have:
>
> Query::=Expression
> Expression::=( OperatorExpr | IfThenElse | FLWOGR | QuantifiedExpression )
>
> If this specification in SQLPP is not intentionally designed, can we
change
> it to this:
>
> Query::=( Expression )
> Expression::=( OperatorExpr | CaseExpr | QuantifiedExpression |
> SelectExpression ) ?
>
> As the Subquery are handled separately in the parenthesized expression
> part, the "SelectExpression" here is non-subquery by default.
>
> Any thoughts? Thanks!
>
> Best,
> Xikui
>
