public ASTNode getAST() {
      ASTBuilder b = ASTBuilder
          .construct(HiveParser.TOK_QUERY, "TOK_QUERY")
          .add(from)
          .add(
              ASTBuilder.construct(HiveParser.TOK_INSERT, "TOK_INSERT").add(ASTBuilder.destNode())
                  .add(select).add(where).add(groupBy).add(having).add(distributeBy).add(order).add(limit));
      return b.node();
    }
Assumption:<br>
1. Project will always be child of Sort.<br>
2. In Calcite every projection in Project is uniquely named
(unambiguous) without using table qualifier (table name).<br>

@param order
         Hive Sort Node
@return Schema
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/translator/ASTConverter.java