message: Remove unused parent property.
diff: @@ -37,13 +37,13 @@ class AggregateExpression;
  class Expression : public Printable {
  public:
  //! Create an Expression
  - Expression(ExpressionType type) : type(type), parent(nullptr) {}
  + Expression(ExpressionType type) : type(type) {}
  //! Create an Expression with zero, one or two children with the
  //! specified return type
  Expression(ExpressionType type, TypeId return_type,
  std::unique_ptr<Expression> left = nullptr,
  std::unique_ptr<Expression> right = nullptr)
  - : type(type), return_type(return_type), parent(nullptr) {
  + : type(type), return_type(return_type) {
  if (left)
  AddChild(std::move(left));
  if (right)
  @@ -67,7 +67,6 @@ class Expression : public Printable {
  //! Add a child node to the Expression. Note that the order of
  //! adding children is important in most cases
  void AddChild(std::unique_ptr<Expression> child) {
  - child->parent = this;
  children.push_back(std::move(child));
  }
  @@ -161,9 +160,6 @@ class Expression : public Printable {
  //! 1 AS f)
  std::string alias;
  - //! The parent node of the expression, if any
  - Expression *parent;
  -
  //! A list of children of the expression
  std::vector<std::unique_ptr<Expression>> children;
  };
  