public ASTNode getUnionAllAST(ASTNode leftAST, ASTNode rightAST) {

    ASTNode unionTokAST = ASTBuilder.construct(HiveParser.TOK_UNIONALL, "TOK_UNIONALL").add(leftAST)
        .add(rightAST).node();

    return unionTokAST;
  }
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