MOD: WHERE grammar
ADD: some constants for operator
ADD: Boolean Expression
A boolean expression is a tree
root and internal nodes should be operator(and, or, not)
subnode should also be boolean expression
leaf node must be the BoolValue, which is the only type without children
ADD: Predicate Node
Boolean value should be a predicate expression, which has op and operand
PredicateOp: > = < ...
PredicateOperand: table.column or literal value
ADD: listener for where and examples of parsing WHERE condition