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From Xikui Wang <>
Subject Specification of "Expression" in SQLPP
Date Thu, 15 Mar 2018 03:59:45 GMT
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:

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!


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