message: Add DISTINCT to AggregateExpression::ToString
diff: @@ -37,7 +37,7 @@ AggregateExpression::AggregateExpression(ExpressionType type, bool distinct, uni
  }
  string AggregateExpression::ToString() const {
  - return ExpressionTypeToString(type) + "(" + (child ? child->ToString() : string()) + ")";
  + return ExpressionTypeToString(type) + "(" + (distinct ? "DISTINCT " : " " ) + (child ? child->ToString() : string()) + ")";
  }
  bool AggregateExpression::Equals(const BaseExpression *other_) const {
  